Intelligent thermostat system for load monitoring a refrigerant-cycle apparatus

ABSTRACT

A real-time monitoring system that monitors various aspects of the operation of a refrigerant-cycle system is described. In one embodiment, the system includes a processor that measures power provided to the refrigerant-cycle system and that gathers data from one or more sensors and uses the sensor data to calculate a figure of merit related to the efficiency of the system. In one embodiment, the sensors include one or more of the following sensors: a suction line temperature sensor, a suction line pressure sensor, a suction line flow sensor, a hot gas line temperature sensor, a hot gas line pressure sensor, a hot gas line flow sensor, a liquid line temperature sensor, a liquid line pressure sensor, a liquid line flow sensor. In one embodiment, the sensors include one or more of an evaporator air temperature input sensor, an evaporator air temperature output sensor, an evaporator air flow sensor, an evaporator air humidity sensor, and a differential pressure sensor. In one embodiment, the sensors include one or more of a condenser air temperature input sensor, a condenser air temperature output sensor, and a condenser air flow sensor, an evaporator air humidity sensor. In one embodiment, the sensors include one or more of an ambient air sensor and an ambient humidity sensor.

REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 11/130,562, filed May 17, 2005, titled “INTELLIGENT THERMOSTATSYSTEM FOR MONITORING A REFRIGERANT-CYCLE APPARATUS, which is acontinuation application of U.S. application Ser. No. 10/916,222, filedAug. 11, 2004, titled “METHOD AND APPARATUS FOR MONITORINGREFRIGERANT-CYCLE SYSTEMS,” the entire contents of which are herebyincorporated by reference.

BACKGROUND

1. Field of the Invention

The invention relates to monitoring system for measuring the operatingand efficiency of a refrigerant-cycle system, such as, for example, anair conditioning system or refrigeration system.

2. Description of the Related Art

One of the major recurring expenses in operating a home or commercialbuilding is the cost of providing electricity to the Heating VentilatingAir Conditioning (HVAC) system. If the HVAC system is not operating atpeak efficiency, then the cost of operating the system increasesunnecessarily. Each pound of refrigerant circulating in the system mustdo its share of the work. It must absorb an amount of heat in theevaporator or cooling coil, and it must dissipate this heat-plus somethat is added in the compressor-through the condenser, whether aircooled, water cooled, or evaporative cooled. The work done by each poundof the refrigerant as it goes through the evaporator is reflected by theamount of heat it picks up from the refrigeration load, chiefly when therefrigerant undergoes a change of state from a liquid to a vapor.

For a liquid to be able to change to a vapor, heat must be added to orabsorbed in it. This is what happens in the cooling coil. Therefrigerant enters the metering device as a liquid and passes throughthe device into the evaporator, where it absorbs heat as it evaporatesinto a vapor. As a vapor, it makes its way through the suction tube orpipe to the compressor. Here it is compressed from a low temperature,low pressure vapor to a high temperature, high pressure vapor; then itpasses through the high pressure or discharge pipe to the condenser,where it undergoes another change of state—from a vapor to a liquid—inwhich state it flows out into the liquid pipe and again makes its way tothe metering device for another trip through the evaporator.

When the refrigerant, as a liquid, leaves the condenser it may go to areceiver until it is needed in the evaporator; or it may go directlyinto the liquid line to the metering device and then into the evaporatorcoil. The liquid entering the metering device just ahead of theevaporator coil will have a certain heat content (enthalpy), which isdependent on its temperature when it enters the coil, as shown in therefrigerant tables in the Appendix. The vapor leaving the evaporatorwill also have a given heat content (enthalpy) according to itstemperature, as shown in the refrigerant tables.

The difference between these two amounts of heat content is the amountof work being done by each pound of refrigerant as it passes through theevaporator and picks up heat. The amount of heat absorbed by each poundof refrigerant is known as the refrigerating effect of the system, or ofthe refrigerant within the system.

Situations that can reduce the overall efficiency of the system include,refrigerant overcharge, refrigerant undercharge, restrictions inrefrigerant lines, faulty compressor, excessive load, insufficient load,undersized or dirty duct work, clogged air filters, etc.

Unfortunately, modern HVAC systems do not include monitoring systems tomonitor the operating of the system. A modern HVAC system is typicallyinstalled, charged with refrigerant by a service technician, and thenoperated for months or years without further maintenance. As long as thesystem is putting out cold air, the building owner or home owner assumethe system is working properly. This assumption can be expensive; as theowner has no knowledge of how well the system is functioning. If theefficiency of the system deteriorates, the system may still be able toproduce the desired amount of cold air, but it will have to work harder,and consume more energy, to do so. In many cases, the system owner doesnot have the HVAC system inspected or serviced until the efficiency hasdropped so low that it can no longer cool the building. This is due inpart, because servicing of an HVAC system requires specialized tools andknowledge that the typical building owner or home owner does not posses.Thus, the building owner or home owner, must pay for an expensiveservice call in order to have the system evaluated. Even if the ownerdoes pay for a service call, many HVAC service technicians do notmeasure system efficiency. Typically, the HVAC service technicians aretrained only to make rudimentary checks of the system (e.g., refrigerantcharge, output temperature), but such rudimentary checks may not uncoverother factors that can cause poor system efficiency. Thus, the typicalbuilding owner, or home owner, operates the HVAC system year after yearnot knowing that the system may be wasting money by operating at lessthan peak efficiency. Moreover, inefficiency use of electrical power canlead to brownouts and blackouts during heat waves or other periods ofhigh air conditioning usage due to overloading of the electric powersystem (commonly referred to as the electric power grid).

SUMMARY

These and other problems are solved by a real-time monitoring systemthat monitors various aspects of the operation of a refrigerant system,such as, for example, an HVAC system, a refrigerator, a cooler, afreezer, a water chiller, etc. In one embodiment, the monitoring systemis configured as a retrofit system that can be installed in an existingrefrigerant system.

In one embodiment, the system includes a processor that measures powerprovided to the HVAC system and that gathers data from one or moresensors and uses the sensor data to calculate a figure of merit relatedto the efficiency of the system. In one embodiment, the sensors includeone or more of the following sensors: a suction line temperature sensor,a suction line pressure sensor, a suction line flow sensor, a hot gasline temperature sensor, a hot gas line pressure sensor, a hot gas lineflow sensor, a liquid line temperature sensor, a liquid line pressuresensor, a liquid line flow sensor. In one embodiment, the sensorsinclude one or more of an evaporator air temperature input sensor, anevaporator air temperature output sensor, an evaporator air flow sensor,an evaporator air humidity sensor, and a differential pressure sensor.In one embodiment, the sensors include one or more of a condenser airtemperature input sensor, a condenser air temperature output sensor, anda condenser air flow sensor, an evaporator air humidity sensor. In oneembodiment, the sensors include one or more of an ambient air sensor andan ambient humidity sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a typical refrigerant cycle system used in HVACsystems, refrigerators, freezers, and the like.

FIG. 2 is a detailed pressure-heat diagram of a typical refrigerant(R-22).

FIG. 3 is a pressure-heat diagram showing pressure-enthalpy changesthrough a refrigeration cycle.

FIG. 4 is a pressure-heat diagram showing pressure, heat, andtemperature values for a refrigeration cycle operating with a 40° F.evaporator.

FIG. 5 is a pressure-heat diagram showing pressure, heat, andtemperature values for a refrigeration cycle operating with a 20° F.evaporator.

FIG. 6 is a pressure-heat diagram showing the cycle of FIG. 4 with a 40°F. evaporating temperature, where the condensing temperature has beenincreased to 120° F.

FIG. 7 is a pressure-heat diagram showing how subcooling by thecondenser improves the refrigeration effect and the COP.

FIG. 8 is a pressure-heat diagram showing the cooling process in theevaporator.

FIG. 9A is a block diagram of a monitoring system for monitoring theoperation of the refrigerant-cycle system.

FIG. 9B is a block diagram of a monitoring system for monitoring theoperation of the refrigerant-cycle system, where operating data for thesystem is provided to a monitoring service, such as, for example, apower company or monitoring center, by using data transmission overpower lines.

FIG. 9C is a block diagram of a monitoring system for monitoring theoperation of the refrigerant-cycle system, where operating data for thesystem is provided to a monitoring service, such as, for example, apower company or monitoring canter, by using data transmission over acomputer network.

FIG. 9D is a block diagram of a monitoring system for monitoring theoperation of the refrigerant-cycle system, where data regardingoperation of the system is provided to a thermostat and/or to a computersystem such as, for example, a site monitoring computer, a maintenancecomputer, a personal digital assistant, a personal computer, etc.

FIG. 9E is a block diagram of a monitoring system for monitoring theoperation of the refrigerant-cycle system wherein anelectronically-controlled metering device is provided to allow controlof the system in an energy-efficient matter.

FIG. 9F is a block diagram of a thermostat control and monitoring systemhaving a data interface device provided to the thermostat.

FIG. 9G is a block diagram of a thermostat control and monitoring systemhaving a data interface device provided to the evaporator unit.

FIG. 9H is a block diagram of a thermostat control and monitoring systemhaving a data interface device provided to the condenser unit.

FIG. 10 (consisting of FIGS. 10A and 10B) shows various sensors that canbe used in connection with the system of FIGS. 9A-H for monitoring theoperation of the refrigerant-cycle system.

FIG. 11 shows the temperature drop across in the air through theevaporator as a function of humidity.

FIG. 12 shows heat capacity of a typical refrigerant-cycle system as afunction of refrigerant charge.

FIG. 13 shows power consumed in a typical refrigerant-cycle system as afunction of refrigerant charge.

FIG. 14 shows efficiency of a typical refrigerant-cycle system as afunction of refrigerant charge.

FIG. 15 shows a differential-pressure sensor used to monitor an airfilter in an air-handler system.

FIG. 16 shows a differential-pressure sensor used to monitor an airfilter in an air-handler system using a wireless system to providefilter differential pressure data back to other aspects of themonitoring system.

FIG. 17 shows the system of FIG. 16 implemented using a filter frame tofacilitate retrofitting of existing air handler systems.

DETAILED DESCRIPTION

FIG. 1 is a diagram of a typical refrigerant cycle system 100 used inHVAC systems, refrigerators, freezers, and the like. In the system 100,a compressor provides hot compressed refrigerant gas to a hot gas line106. The hot gas line provides the hot gas to a condenser 107. Thecondenser 107 cools the gas and condenses the gas into a liquid that isprovided to a liquid line 108. The liquid refrigerant in the liquid line108 is provided through a metering device 109 to an evaporator 110. Therefrigerant expands back into a gas in the evaporator 110 and isprovided back to the compressor though a suction line 110. A suctionservice valve 120 provides access to the suction line 111. A liquid lineservice valve 121 provides access to the liquid line 121. A fan 123provides input air 124 to the evaporator 110. The evaporator cools theair and provides cooled evaporator output air 125. An optionaldrier/accumulator 130 can be provided in the liquid line 108. A fan 122provides cooling air to the condenser 107.

The metering device 109 can be any refrigerant metering device as usedin the art, such as, for example, a capillary tube, a fixed orifice, aThermostatic eXpansion Valve (TXV), an electronically controlled valve,a pulsating solenoid valve, a stepper-motor valve, a low side float, ahigh-side float, an automatic expansion valve, etc. A fixed meteringdevice such as a capillary tube or fixed orifice will allow someadjustment in system capacity as the load changes. As the outdoorcondensing temperature increases, more refrigerant is fed through themetering device into the evaporator, increasing its capacity slightly.Conversely, as the heat load goes down, the outdoor condensingtemperature goes down and less refrigerant is fed into the evaporator.For a location where the load does not vary widely, fixed meteringdevices my float with the load well enough. However, for climates wherethere is a relatively greater range in temperature variation, anadjustable metering device is typically used.

The system 100 cools the air through the evaporator 110 by using therefrigerating effect of an expanding gas. This refrigerating effect israted in Btu per pound of refrigerant (Btu/lb); if the total heat loadis known (given in Btu/hr), one can find the total number of pounds ofrefrigerant that must be circulated each hour of operation of thesystem. This figure can be broken down further to the amount that mustbe circulated each minute, by dividing the amount circulated per hour by60.

Because of a small orifice in the metering device 109, when thecompressed refrigerant passes from the smaller opening in the meteringdevice to the larger tubing in the evaporator, a change in pressureoccurs together with a change in temperature. This change in temperatureoccurs because of the vaporization of a small portion of the refrigerant(about 20%) and, in the process of this vaporization, the heat that isinvolved is taken from the remainder of the refrigerant.

For example, from the table of saturated R-22 in FIG. 2, it can be seenthat the heat content of 100° F. liquid is 39.27 BTU/lb and that of 40°F. liquid is 21.42 BTU/lb; this indicates that 17.85 BTU/lb has to beremoved from each pound of refrigerant entering the evaporator. Thelatent heat of vaporization of 40° F. (17.85 BTU/lb) is 68.87 BTU/lb.This is another method of calculating the refrigerating effect, or workbeing done, by each pound of refrigerant under the conditions given.

The capacity of the compressor 105 should be such that it will removefrom the evaporator that amount of refrigerant which has vaporized inthe evaporator and in the metering device in order to get the necessarywork done. The compressor 105 must be able to remove and send on to thecondenser 107 the same weight of refrigerant vapor, so that it can becondensed back into a liquid and so continue in the refrigerationcircuit 100 to perform additional work.

If the compressor 105 is unable to move this weight, some of the vaporwill remain in the evaporator 110. This, in turn, will cause an increasein pressure inside the evaporator 110, accompanied by an increase intemperature and a decrease in the work being done by the refrigerant,and design conditions within the refrigerated space cannot bemaintained.

A compressor 105 that is too large will withdraw the refrigerant fromthe evaporator 110 too rapidly, causing a lowering of the temperatureinside the evaporator 110, so that design conditions will not bemaintained.

In order for design conditions to be maintained within a refrigerationcircuit, a balance between the requirements of the evaporator 110 andthe capacity of the compressor 105 is maintained. This capacity isdependent on its displacement and on its volumetric efficiency.Volumetric efficiency depends on the absolute suction and dischargepressures under which the compressor 105 is operating.

In one embodiment, the system 1000 controls the speed of the compressor105 to increase efficiency. In one embodiment, the system 1000 controlsthe metering device 109 to increase efficiency. In one embodiment, thesystem 1000 controls the speed of the fan 123 to increase efficiency. Inone embodiment, the system 1000 controls the speed of the fan 122 toincrease efficiency.

In the system 100, the refrigerant passes from the liquid stage into thevapor stage as it absorbs heat in the evaporator 110 coil. In thecompressor 105 ion stage, the refrigerant vapor is increased intemperature and pressure, then the refrigerant gives off its heat in thecondenser 107 to the ambient cooling medium, and the refrigerant vaporcondenses back to its liquid state where it is ready for use again inthe cycle.

FIG. 2 shows the pressure, heat, and temperature characteristics of thisrefrigerant. Enthalpy is another word for heat content. Diagrams such asFIG. 2 are referred to as pressure-enthalpy diagrams. Detailedpressure-enthalpy diagrams can be used for the plotting of the cycleshown in FIG. 2, but a basic or skeleton chart as shown in FIG. 3 isuseful as a preliminary illustration of the various phases of therefrigerant circuit. There are three basic areas on the chart denotingchanges in state between the saturated liquid line 301 and saturatedvapor line 302 in the center of the chart. The area to the left of thesaturated liquid line 301 is the subcooled area, where the refrigerantliquid has been cooled below the boiling temperature corresponding toits pressure; whereas the area to the right of the saturated vapor line302 is the area of superheat, where the refrigerant vapor has beenheated beyond the vaporization temperature corresponding to itspressure.

The construction of the diagram 300, illustrates what happens to therefrigerant at the various stages within the refrigeration cycle. If theliquid vapor state and any two properties of a refrigerant are known andthis point can be located on the chart, the other properties can bedetermined from the chart.

If the point is situated anywhere between the saturated liquid 310 andvapor lines 302, the refrigerant will be in the form of a mixture ofliquid and vapor. If the location is closer to the saturated liquid line301, the mixture will be more liquid than vapor, and a point located inthe center of the area at a particular pressure would indicate a 50%liquid 50% vapor situation.

The change in state from a vapor to a liquid, the condensing process,occurs as the path of the cycle develops from right to left; whereas thechange in state from a liquid to a vapor, the evaporating process,travels from left to right. Absolute pressure is indicated on thevertical axis at the left, and the horizontal axis indicates heatcontent, or enthalpy, in BTU/lb.

The distance between the two saturated lines 310, 302 at a givenpressure, as indicated on the heat content line, amounts to the latentheat of vaporization of the refrigerant at the given absolute pressure.The distance between the two lines of saturation is not the same at allpressures, for they do not follow parallel curves. Therefore, there arevariations in the latent heat of vaporization of the refrigerant,depending on the absolute pressure. There are also variations inpressure-enthalpy charts of different refrigerants and the variationsdepend on the various properties of the individual refrigerants.

There is relatively little temperature change of the condensedrefrigeration liquid after it leaves the condenser 107 and travelsthrough the liquid line 108 on its way to the expansion or meteringdevice 109, or in the temperature of the refrigerant vapor after itleaves the evaporator 110 and passes through the suction line 111 to thecompressor 105.

FIG. 4 shows the phases of the simple saturated cycle with appropriatelabeling of pressures, temperatures, and heat content or enthalpy.Starting at point A on the saturated liquid where all of the refrigerantvapor at 100° F. has condensed into liquid at 100° F. and is at theinlet to the metering device, between points A and B is the expansionprocess as the refrigerant passes through the metering device 109; andthe refrigerant temperature is lowered from the condensation temperatureof 100° F. to the evaporating temperature of 40° F.

When the vertical line A-B (the expansion process) is extended downwardto the bottom axis, a reading of 39.27 BTU/lb is indicated, which is theheat content of 100° F. liquid. To the left of point B at the saturatedliquid line 108 is point Z, which is also at the 40° F. temperatureline. Taking a vertical path downward from point Z to the heat contentline, a reading of 21.42 BTU/lb is indicated, which is the heat contentof 40° F. liquid.

The horizontal line between points B and C indicates the vaporizationprocess in the evaporator 110, where the 40° F. liquid absorbs enoughheat to completely vaporize the refrigerant. Point C is at the saturatedvapor line, indicating that the refrigerant has completely vaporized andis ready for the compression process. A line drawn vertically downwardto where it joins the enthalpy line indicates that the heat content,shown at h_(c) is 108.14 Btu/lb, and the difference between h_(a) andh_(c) is 68.87 Btu/lb, which is the refrigerating effect, as shown in anearlier example.

The difference between points h_(z) and h_(c) on the enthalpy lineamounts to 86.72 Btu/lb, which is the latent heat of vaporization of 1lb of R-22 at 40° F. This amount would also exhibit the refrigeratingeffect, but some of the refrigerant at 100° F. must evaporate orvaporize in order that the remaining portion of each pound of R-22 canbe lowered in temperature from 100° F. to 40° F.

All refrigerants exhibit properties of volume, temperature, pressure,enthalpy or heat content, and entropy when in a gaseous state. Entropyis defined as the degree of disorder of the molecules that make up. Inrefrigeration, entropy is the ratio of the heat content of the gas toits absolute temperature in degrees Rankin.

The pressure-enthalpy chart plots the line of constant entropy, whichstays the same provided that the gas is compressed and no outside heatis added or taken away. When the entropy is constant, the compressionprocess is called adiabatic, which means that the gas changes itscondition without the absorption or rejection of heat either from or toan external body or source. It is common practice, in the study ofcycles of refrigeration, to plot the compression line either along orparallel to a line of constant entropy.

In FIG. 5, line C-D denotes the compression process, in which thepressure and temperature of the vapor are increased from that in theevaporator 110 to that in the condenser 107, with the assumption thatthere has been no pickup of heat in the suction line 111 between theevaporator 110 and the compressor 105. For a condensing temperature of100° F., a pressure gauge would read approximately 196 psig; but thechart is rated in absolute pressure and the atmospheric pressure of 14.7are added to the psig, making it actually 210.61 psia.

Point D on the absolute pressure line is equivalent to the 100° F.condensing temperature; it is not on the saturated vapor line, it is tothe right in the superheat area, at a junction of the 210.61 psia line,the line of constant entropy of 40° F., and the temperature line ofapproximately 128° F. A line drawn vertically downward from point Dintersects the heat content line at 118.68 Btu/lb, which is h_(d), thedifference between h_(c) and hd, is 10.54 Btu/lb—the heat of compressionthat has been added to the vapor. This amount of heat is the heat energyequivalent of the work done during the refrigeration compression cycle.This is the theoretical discharge temperature, assuming that saturatedvapor enters the cycle; in actual operation, the discharge temperaturemay be 20° to 35° higher than that predicted theoretically. This can bechecked in the system 100 by attaching a temperature sensor 1016 to thehot gas line 106.

During the compression process, the vapor is heated by the action of itsmolecules being pushed or compressed closer together, commonly calledheat of compression.

Line D-E denotes the amount of superheat that must be removed from thevapor before it can commence the condensation process. A line drawnvertically downward from point E to point h_(e) on the heat content lineindicates the distance h_(d)-h_(e), or heat amounting to 6.54 Btu/lb,since the heat content of 100° F. vapor is 112.11 Btu/lb. This superheatis usually removed in the hot gas discharge line or in the upper portionof the condenser 107. During this process the temperature of the vaporis lowered to the condensing temperature.

Line E-A represents the condensation process that takes place in thecondenser 107. At point E the refrigerant is a saturated vapor at thecondensing temperature of 100° F. and an absolute pressure of 210.61psia; the same temperature and pressure prevail at point A, but therefrigerant is now in a liquid state. At any other point on line E-A therefrigerant is in the phase of a liquid vapor combination; the closerthe point is to A, the greater the amount of the refrigerant that hascondensed into its liquid stage. At point A, each pound of refrigerantis ready to go through the refrigerant cycle again as it is needed forheat removal from the load in the evaporator 110.

Two factors that determine the coefficient of performance (COP) of arefrigerant are refrigerating effect and heat of compression. Theequation may be written as

$\begin{matrix}{{COP} = \frac{refrigerating\_ effect}{{heat\_ of}{\_ compression}}} & (1)\end{matrix}$Substituting values, from the pressure-enthalpy diagram of the simplesaturated cycle previously presented, the equation would be:

${COP} = {\frac{h_{c} - h_{a}}{h_{d} - h_{c}} = {\frac{68.87}{10.54} = 6.53}}$

The COP is, therefore, a rate or a measure of the theoretical efficiencyof a refrigeration cycle is the energy that is absorbed in theevaporation process divided by the energy supplied to the gas during thecompression process. As can be seen from Equation 1, the less energyexpended in the compression process, the larger will be the COP of therefrigeration system.

The pressure-enthalpy diagrams in FIGS. 4 and 5 show a comparison of twosimple saturated cycles having different evaporating temperatures, tobring out various differences in other aspects of the cycle. In orderthat an approximate mathematical calculation comparison may be made, thecycles shown in FIGS. 4 and 5 will have the same condensing temperature,but the evaporating temperature will be lowered 20° F. The values of A,B, C, D, and E from FIG. 4 as the cycle are compared to that in FIG. 5(with a 20° F. evaporator 110). The refrigerating effect, heat ofcompression, and the heat dissipated at the condenser 107 in each of therefrigeration cycles will be compared. The comparison will be based ondata about the heat content or enthalpy line, rated in Btu/lb.

For the 20° F. evaporating temperature cycle shown in FIG. 5:

Net refrigerating effect (h_(c′)-h_(a))=67.11 Btu/lb

Heat of compression (h_(d′)-h_(c′))=67.11 Btu/lb

Comparing the data above with those of the cycle with the 40° F.evaporating temperature FIG. 4, shows that there is a decrease in thenet refrigeration effect (NRE) of 2.6% and an increase in the heat ofcompression of 16.7%. There will be some increase in superheat, whichshould be removed either in the hot gas line 106 or the upper portion ofthe condenser 107. This is the result of a lowering in the suctiontemperature, the condensing temperature remaining the same.

From Equation 1, it follows that the weight of refrigerant to becirculated per ton of cooling, in a cycle with a 20° F. evaporatingtemperature and a 100° F. condensing temperature, is 2.98 lb/min/ton:

$\begin{matrix}{W = \frac{200\mspace{11mu}\left( {{Btu}\text{/}\min} \right)}{{NRE}\mspace{11mu}\left( {{Btu}\text{/}{lb}} \right)}} \\{= \frac{200\mspace{11mu}{Btu}\text{/}\min}{67.11\mspace{11mu}{Btu}\text{/}{lb}}} \\{= {2.98\mspace{11mu}{lb}\text{/}\min}}\end{matrix}$

Circulating more refrigerant typically involves either a largercompressor 105, or the same size of compressor 105 operating at a higherrpm.

FIG. 6 shows the original cycle with a 40° F. evaporating temperature,but the condensing temperature has been increased to 120° F.

Again taking the specific data from the heat content or enthalpy line,one now finds for the 120° F. condensing temperature cycle thath_(a)=45.71, h_(c)=108.14, h_(d)=122.01, and h_(e)=112.78. Thus, the netrefrigerating effect (h_(c)-h_(a′))=62.43 Btu/lb, the heat ofcompression (h_(d′)-h_(c))=13.87 Btu/lb, and the condenser 107 superheat(h_(d′)-h_(e′))=9.23 Btu/lb

In comparison with the cycle having the 100° F. condensing temperature(FIG. 4), the cycle can also be calculated by allowing the temperatureof the condensing process to increase to 120° F. (as shown in FIG. 7).FIG. 7 shows a decrease in the NRE of 9.4%, an increase in heat ofcompression of 31.6%, and an increase of superheat to be removed eitherin the discharge line or in the upper portion of the condenser 107 of40.5%.

With a 40° F. evaporating temperature and a 120° F. condensingtemperature, the weight of refrigerant to be circulated will be 3.2lb/min/ton. This indicates that approximately 10% more refrigerant mustbe circulated to do the same amount of work as when the condensingtemperature was 100° F.

Both of these examples show that for the beset efficiency of a system,the suction temperature should be as high as feasible, and thecondensing temperature should be as low as feasible. Of course, thereare limitations as to the extremes under which the system 100 mayoperate satisfactorily, and other means of increasing efficiency mustthen be considered. Economics of equipment (cost+operating performance)ultimately determine the feasibility range.

Referring to FIG. 8, after the condensing process has been completed andall of the refrigerant vapor at 120° F. is in the liquid state, if theliquid can be subcooled to point A′ on the 100° F. line (a difference of20° F.), the NRE (h_(c)-h_(a)) will be increased 6.44 Btu/lb. Thisincrease in the amount of heat absorbed in the evaporator 110 without anincrease in the heat of compression will increase the COP of the cycle,since there is no increase in the energy input to the compressor 105.

This subcooling can take place while the liquid is temporarily instorage in the condenser 107 or receiver, or some of the liquid's heatmay be dissipated to the ambient temperature as it passes through theliquid pipe on its way to the metering device. Subcooling can also takeplace in a commercial type water cooled system through the use of aliquid subcooler.

Normally, the suction vapor does not arrive at the compressor 105 in asaturated condition. Superheat is added to the vapor after theevaporating process has been completed, in the evaporator 110 and/or inthe suction line 111, as well as in the compressor 105. If thissuperheat is added only in the evaporator 110, it is doing some usefulcooling; for it too is removing heat from the load or product, inaddition to the heat that was removed during the evaporating process.But if the vapor is superheated in the suction line 111 located outsideof the conditioned space, no useful cooling is accomplished; yet this iswhat takes place in many system.

In the system 100, the refrigerant pressure is relatively high in thecondenser 107 and relatively low in the evaporator 110. A pressure riseoccurs across the compressor 105 and a pressure drop occurs across themetering device 109. Thus, the compressor 105 and the metering devicemaintain the pressure difference between the condenser 107 and theevaporator 110.

Thus, a refrigeration system can be divided into the high side and lowside portions. The high side contains the high pressure vapor and liquidrefrigerant and is the part of the system that rejects heat. The lowside contains the low pressure liquid vapor and refrigerant and is theside that absorbs heat.

Heat is always trying to reach a state of balance by flowing from awarmer object to a cooler object. Heat only flows in one direction, fromwarmer to cooler. Temperature difference (TD) is what allows heat toflow from one object to another. The greater the temperature differencethe more rapid the heat flow. For the high side of a refrigeration unitto reject heat its temperature must be above the ambient or surroundingtemperature. For the evaporator 110 to absorb heat, its temperature mustbe below the surrounding ambient temperature.

Two factors that affect the quantity of heat transferred between twoobjects are the temperature difference and the mass of the two objects.The greater the temperature difference between the refrigerant coil(e.g., the condenser 107 or the evaporator 110) and the surrounding air,the more rapid will be the heat transfer. The larger the size of therefrigerant coil, the greater the mass of refrigerant, which alsoincreases the rate of heat transfer. Engineers can either design coilsto have high temperature differences or larger areas to increase theheat transfer rate.

To increase energy efficiency, systems are designed with larger coilsbecause it is more efficient to have a lower temperature and a largerarea to transfer heat. It takes less energy to produce a smallerpressure/temperature difference within a refrigeration system.Manufacturers of new high efficiency air conditioning systems use thisprinciple.

The same principle can be applied to the evaporator 110 coils. Thetemperature differences between the evaporator input air 124 and theevaporator output air 125 are lower than they were on earlier systems.Older, lower efficiency, air conditioning systems may have evaporativecoils that operate at 35° F. output temperature, while newer higherefficiency evaporator 110 may operate in the 45° F. output range. Bothevaporators 110 can pick up the same amount of heat provided that thehigher temperature, higher efficiency coil has greater area and,therefore, more mass of refrigerant being exposed to the air stream toabsorb heat. The higher evaporative coil temperature may produce lessdehumidification. In humid climates, de-humidification can be animportant part of the total air conditioning.

Correct equipment selection is important to ensure system operation andto obtain desired energy efficiencies. Previously, it was a commonpractice in many locations for installers to select an evaporator 110 ofa different tonnage than the condenser unit 101 capacity. While thispractice in the past may provide higher efficiencies, for most oftoday's more technically designed systems proper matching is usuallyachieved by using the manufacturer's specifications in order to provideproper operation. Mismatching systems can result in poor humiditycontrol and higher operating costs. In addition to poor energyefficiency and lack of proper humidity control, the compressor 105 in amismatched system may not receive adequate cooling from returningrefrigerant vapor. As a result the compressor 105 temperature will behigher, and this can reduce the life of the compressor 105.

As refrigerant vapor leaves the discharge side of a compressor 105, itenters the condenser 107. As this vapor travels through the condenser107, heat from the refrigerant dissipates to the surrounding air throughthe piping and fins. As heat is removed, the refrigerant begins tochange state from vapor to liquid. As the mixture of liquid and vaporcontinues to flow through the condenser 107, more heat is removed andeventually all, or virtually all, of the vapor has transformed intoliquid. The liquid flows from the outlet of the condenser 107 throughthe liquid line 108 to the metering device 109.

The high pressure, high temperature liquid refrigerant passes throughthe metering device 109 where its temperature and pressure change. Asthe pressure and temperature change, some of the liquid refrigerantboils off forming flash gas. As this mixture of refrigerant, liquid, andvapor flow through the evaporator 110, heat is absorbed, and theremaining liquid refrigerant changes into a vapor. At the outlet of theevaporator 110 the vapor flows back through the suction line 111 to thecompressor 105.

The compressor 105 draws in this low pressure, low temperature vapor andconverts it to a high temperature, high pressure vapor where the cyclebegins again.

An ideally sized and functioning system 100 is one where the last bit ofrefrigerant vapor changes into a liquid at the end of the condenser 107and where the last bit of liquid refrigerant changes into a vapor at theend of the evaporator 110. However, because it is impossible to have asystem operate at this ideal state, units are designed to have someadditional cooling, called subcooling, of the liquid refrigerant toensure that no vapor leaves the condenser 107. Even a small amount ofvapor leaving a condenser 107 can significantly reduce efficiency of thesystem 100.

On the evaporator 110 side a small amount of additional temperature isadded to the refrigerant vapor, called superheat, to ensure that noliquid refrigerant returns to the compressor 105. Returning liquidrefrigerant to the compressor 105 can damage the compressor 105.

Systems that must operate under a broad range of temperature conditionswill have difficulty maintaining the desired level of subcooling andsuperheat. There are two components that can be used in these systems toenhance the level of efficiency and safety in operation. They are thereceiver and the accumulator. The receiver is placed in the liquid line108 and holds a little extra refrigerant so the system has enough forhigh loads on hot days. The accumulator is placed in the suction line111 and traps any the liquid refrigerant that would flow back to thecompressor 105 on cool days with light loads.

A liquid receiver can be located at the end of the condenser 107 outletto collect liquid refrigerant. The liquid receiver allows the liquid toflow into the receiver and any vapor collected in the receiver to flowback into the condenser 107 to be converted back into a liquid. The lineconnecting the receiver to the condenser 107 is called the condensateline and must be large enough in diameter to allow liquid to flow intothe receiver and vapor to flow back into the condenser 107. Thecondensate line must also have a slope toward the receiver to allowliquid refrigerant to freely flow from the condenser 107 into thereceiver. The outlet side of the receiver is located at the bottom wherethe trapped liquid can flow out of the receiver into the liquid line.

Receivers should be sized so that all of the refrigerant charge can bestored in the receiver. Some refrigeration condensing units come withreceivers built into the base of the condensing unit

The accumulator is located at the end of the evaporator 110 and allowsliquid refrigerant to be collected in the bottom of the accumulator andremain there as the vapor refrigerant is returned to the compressor 105.The inlet side of the accumulator is connected to the evaporator 110where any liquid refrigerant and vapor flow in. The outlet of theaccumulator draws vapor through a U shaped tube or chamber. There isusually a small port at the bottom of the U shaped tube or chamber thatallows liquid refrigerant and oil to be drawn into the suction line.Without this small port, refrigerant oil would collect in theaccumulator and not return to the compressor 105. The small port doesallow some liquid refrigerant to enter the suction line. However, it issuch a small amount of liquid refrigerant that it boils off rapidly, sothere is little danger of liquid refrigerant flowing into the compressor105.

Accumulators are often found on heat pumps. During the changeover cycle,liquid refrigerant can flow back out of the outdoor coil. This liquidrefrigerant could cause compressor 105 damage if it were not for theaccumulator, which blocks its return.

The pressure-heat diagram of FIG. 8 shows the cooling process in theevaporator 110. Initially the high pressure liquid is usually subcooled8-10° F. or more. When subcooled liquid from point A flows through theexpansion device 109, its pressure drops to the pressure of theevaporator 110. Approximately 20% of the liquid boils off to gas,cooling the remaining liquid-gas mixture. Its total heat (enthalpy) atpoint B is relatively unchanged from A. No external heat energy has beenexchanged. From points B to C, the remainder of the liquid boils off,absorbing the heat flowing in from the evaporator 110 load (air, water,etc.). At point C, all of the liquid has evaporated and the refrigerantis vapor at the saturation temperature corresponding to the evaporator110 pressure.

The subcooling increases cycle efficiency and can prevent flash gas dueto pressure loss from components, pipe friction, or increase in height.

Many smaller refrigeration systems are designed to have the expansiondevice control the refrigerant flow so the evaporator 110 will heat thevapor beyond saturated conditions and ensure no liquid droplets willenter and possibly damage the compressor 105. It is assumed here for thesake of simplicity there is no pressure drop through the evaporator 110.In reality there are pressure drops which would slightly shift theevaporating and condensing processes from the constant pressure linesshown.

If the evaporator 110 does not have to superheat refrigerant vapor, itcan produce more cooling capacity. On smaller systems the difference isrelatively small and it is more important to protect the compressor 105.On larger systems, an increase in evaporator performance can beimportant. A flooded evaporator 10 absorbs heat from points B to C. Itcan circulate more pounds of refrigerant (more cooling capacity) persquare foot of heat transfer surface.

An undersized evaporator with less heat transfer surface will not handlethe same heat load at the same temperature difference as a correctlysized evaporator. The new balance point will be reached with a lowersuction pressure and temperature. The load will be reduced and thedischarge pressure and temperature will also be reduced. An undersizedevaporator and a reduced hat load both have similar effect on therefrigerant cycle because they both are removing less heat from therefrigerant.

As the ambient temperature increase, the load on the evaporatorincreases. When the load on the evaporator increase, the pressuresincrease. The operating points shift up and to the right on thepressure-heat curve. As the load on the evaporator decreases, the loadon the evaporator decreases, and the pressures decrease. The operatingpoints on the pressure-heat curve shift down. Thus, knowledge of theambient temperature is useful in determining whether the system 100 isoperating efficiency.

FIG. 9A is a block diagram of a monitoring system 900 for monitoring theoperation of the refrigerant-cycle system. In FIG. 9A, one or morecondenser unit sensors 901 measure operating characteristics of theelements of the condenser unit 101, one or more evaporator unit sensors902 measure operating characteristics of the evaporator unit 102, andone or more ambient sensors 903 measure ambient conditions. Sensor datafrom the condenser unit sensors 901, evaporator unit sensors 902, andcondenser unit sensors 903 are provided to a processing system 904. Theprocessing system 904 uses the sensor data to calculate systemefficiency, identify potential performance problems, calculate energyusage, etc. In one embodiment, the processing system 904 calculatesenergy usage and energy costs due to inefficient operation. In oneembodiment, the processing system 904 schedules filter maintenanceaccording to elapsed time and/or filter usage. In one embodiment, theprocessing system 904 identifies potential performance problems, (e.g.,low airflow, Insufficient or unbalanced load, excessive load, lowambient temperature, high ambient temperature, refrigerant undercharge,refrigerant overcharge, liquid line restriction, suction linerestriction, hot gas line restriction, inefficient compressor, etc.). Inone embodiment, the processing system 904 provides plots or charts ofenergy usage and costs. In one embodiment, the processing system 904 themonitoring system provides plots or charts of the additional energycosts due to inefficient operation of the refrigerant-cycle system. Inone embodiment, a thermostat 952 is provided to the processing system904. In one embodiment, the processing system 904 and thermostat 952 arecombined.

FIG. 9B is a block diagram of the system 900 wherein operating data fromthe refrigerant-cycle system is provided to a remote monitoring service950, such as, for example, a power company or monitoring center. In oneembodiment, the system 900 provides operating data related to theoperating efficiency of the refrigerant-cycle system to the remotemonitor 950. In one embodiment, the remote monitoring service providesoperating efficiency data to an electric power company or governmentalagency.

Data can be transmitted from the system 900 to a remote monitoringservice by using data transmission over power lines as shown in FIG. 9Band/or by using data transmission over a data network (e.g., theInternet, a wireless network, a cable modem network, a telephonenetwork, etc.) as shown in FIG. 9B and also as shown in discussed inconnection with FIGS. 9F-H.

FIG. 9D is a block diagram of a monitoring system for monitoring theoperation of the refrigerant-cycle system, where data regardingoperation of the system is provided to a thermostat 952 and/or to acomputer system 953 such as, for example, a site monitoring computer, amaintenance computer, a personal digital assistant, a personal computer,etc.

FIG. 9E is a block diagram of a monitoring system for monitoring theoperation of the refrigerant-cycle system wherein anelectronically-controlled metering device 960 is provided to allowcontrol of the system in an energy-efficient matter.

FIG. 9F is a block diagram of a thermostat control and monitoring systemhaving a data interface device 955 provided to the thermostat 952. Thethermostat 952 typically communicates with an evaporator unit controller953 using relatively low-voltage control wiring. The control unit 953typically provides relays and other control circuits for the air handlerfan, and other systems in the evaporator unit 102. The control wiring isalso provided to a condenser unit controller 954 in the condenser unit101. The controller 954 provides relays and other control circuits forthe compressor 105, the condenser fan, etc. The data interface device955 is provided to the low-voltage control wiring to allow thethermostat 952 to receive control signals from the remote monitor 950.

FIG. 9G is a block diagram of a thermostat control and monitoring systemwherein a data interface device 956 is provided to the controller 954.The data interface device 956 allows the remote monitor 950 tocommunicate with the condenser unit. In one embodiment, the datainterface device 956 allows the remote monitor to read sensor data fromthe condenser unit 101. In one embodiment, the data interface device 956allows the remote monitor to turn off the condenser unit 101. In oneembodiment, the data interface device 956 allows the remote monitor toswitch the compressor 105 to a lower-speed mode. In one embodiment, thedata interface device 956 allows the remote monitor to switch thecondenser unit 101 to a power conservation mode.

FIG. 9H is a block diagram of a thermostat control and monitoring systemwherein a data interface device 957 is provided to the controller 953.

In one embodiment, the data interface devices 955-957 are configured aspower line modems (e.g., using Broadband over Power Line (BPL), or otherpower line networking technology). In one embodiment, the data interfacedevices 955-957 are configured as wireless modems for communicationusing wireless transmission. In one embodiment, the data interfacedevices 955-957 are configured as telephone modems, cable modems,Ethernet modems, or the like, to communicate using a wired network.

In one embodiment, the system 900 provides sensor data from thecondenser unit sensors 901 and/or the evaporator unit sensors 902 to theremote monitoring service 950. In one embodiment, the system 900 usesdata from the condenser unit sensors 901 and/or the evaporator unitsensors 902 to compute an efficiency factor for the refrigerant-cyclesystem and the system 900 provides the efficiency factor to the remotemonitoring service 950. In one embodiment, the system 900 provides powerusage data (e.g., amount of power used) by the refrigerant-cycle systemand the system 900 provides the efficiency factor to the remotemonitoring service 950. In one embodiment, the system 900 provides anidentification code (ID) with the data transmitted to the remote monitor950 to identify the system 900.

In one embodiment, the remote monitor 950 is provided with dataregarding a maximum expected efficiency for the refrigerant-cycle system(e.g., based on the manufacture and design characteristics of therefrigerant-cycle system) such that the remote monitor 950 can ascertainthe relative efficiency (that is, how the refrigerant-cycle system isoperating with respect to its expected operating efficiency). In oneembodiment, the remote monitor 950 provides efficiency data to the powercompany or to a government agency so electric rates can be chargedaccording to the system efficiency. In one embodiment, the homeowner (orbuilding owner) is charged a higher electrical rate for electrical powerprovided to a refrigerant-cycle system that is operating at a relativelylow absolute efficiency. In one embodiment, the homeowner (or buildingowner) is charged a higher electrical rate for electrical power providedto a refrigerant-cycle system that is operating at a relatively lowrelative efficiency. In one embodiment, the homeowner (or buildingowner) is charged an electrical rate according to a combination therelative and absolute efficiency of the refrigerant-cycle system. In oneembodiment, the data provided to the monitoring system 950 is used toprovide notice to the homeowner (or building owner) that therefrigerant-cycle system is operating at a poor efficiency. In oneembodiment, the data provided to the monitoring system 950 is used toprovide notice to the homeowner (or building owner) that therefrigerant-cycle system is operating at a poor efficiency, and that thesystem must be serviced. In one embodiment, the owner is given a warningthat service is needed. If the unit is not serviced (or if efficiencydoes not improve) after a period of time, the system 950 can remotelyshut off the refrigerant-cycle system by sending commands to one or moreof the interface devices 955-957.

In one embodiment, the homeowner (or building owner) is charged a higherelectrical rate for electrical power provided to a refrigerant-cyclesystem that is operating at a relatively low efficiency during aspecified period of time, such as, for example, when the power system ishighly loaded, during peak afternoon cooling periods, during heat waves,during rolling blackouts, etc. In one embodiment, the homeowner (orbuilding owner) is charged a higher electrical rate (a premium rate) forelectrical power provided to a refrigerant-cycle system during aspecified period of time, such as, for example, when the power system ishighly loaded, during peak afternoon cooling periods, during heat waves,during rolling blackouts, etc. In one embodiment, the homeowner (orbuilding owner) can programming the system 900 to receive messages fromthe power company indicating that premium rates are being charged. Inone embodiment, the homeowner (or building owner) can program the system900 to shut down during premium rate periods. In one embodiment, thehomeowner (or building owner) can avoid paying premium rates by allowingthe power company to remotely control operation of the refrigerant-cyclesystem during premium rate times. In one embodiment, the homeowner (orbuilding owner) is only allowed to run the refrigerant-cycle systemduring premium rate periods if the system it operating above aprescribed efficiency.

In one embodiment, the system 900 monitors the amount of time that therefrigerant-cycle system has been running (e.g., the amount of runtimeduring the last day, week, etc.). In one embodiment, the remotemonitoring system can query the system 900 to obtain data regarding theoperating of the refrigerant-cycle system and one or more of the datainterface devices 955-957 will receive the query and send the requesteddata to the monitoring system 950. The query data be, such as, forexample, the efficiency rating of the refrigerant-cycle system (e.g.,the SEER, EER, etc.), the current operating efficiency of therefrigerant-cycle system, the runtime of the system during a specifiedtime period, etc. The system 950 operator (e.g., the power company orpower transmission company), can use the query data to make loadbalancing decisions. Thus, for example the decision regarding whether toinstruct the refrigerant-cycle system to shut down or go into a lowpower mode can be based on the system efficiency (specified efficiency,absolute efficiency, and/or relative efficiency), the amount of time thesystem has been running, the home or building owner's willingness to paypremium rates during load shedding periods, etc. Thus, for example ahomeowner who has a low-efficiency system that is heavily used or whohas indicated an unwillingness to pay premium rates, would have his/herrefrigerant-cycle system shut off by the system 950 before that of ahomeowner who has installed a high-efficiency system that is usedrelatively little, and who had indicated a willingness to pay premiumrates. In one embodiment, in making the decision to shut off the system900, the monitoring system 950 would take into account the efficiency ofthe system 900, the amount the system 900 is being used, and the owner'swillingness to pay premium rates. In one embodiment, higher-efficiencysystems are preferred over lower-efficiency systems (that is,higher-efficiency systems are less likely to be shut off during a poweremergency), and lightly-used systems are preferred over heavily-usedsystems.

In one embodiment, the system 900 sends data regarding the settemperature of the thermostat 952 to the monitoring system 950. In oneembodiment, the electricity rate charged to the homeowner (or buildingowner) calculated according to a set point of the thermostat 952 suchthat a lower set point results in a higher rate charge perkilowatt-hour. In one embodiment, the electricity rate charged to thehomeowner (or building owner) calculated according to the set point ofthe thermostat 952 and the relative efficiency of the refrigerant-cyclesystem such that a lower set point and/or lower efficiency results in ahigher rate charge per kilowatt-hour. In one embodiment, the electricityrate charged to the homeowner (or building owner) calculated accordingto the set point of the thermostat 952 and the absolute efficiency ofthe refrigerant-cycle system such that a lower set point and/or lowerefficiency results in a higher rate charge per kilowatt-hour. In oneembodiment, the electricity rate charged to the homeowner (or buildingowner) calculated according to the set point of the thermostat 952, therelative efficiency of the refrigerant-cycle system, and the absoluteefficiency of the refrigerant-cycle system according to a formulawhereby a lower set point and/or lower efficiency results in a higherrate charge per kilowatt-hour.

In one embodiment, the monitoring system 950 can send instructions tothe system 900 to shut down if the refrigerant-cycle system is operatingat a low efficiency. In one embodiment, the monitoring system 950 cansend instructions to the system 900 to change the setting of thethermostat 952 (e.g., raise the set temperature of the thermostat 952)in response to low efficiency of the refrigerant-cycle system and/or toavoid a blackout. In one embodiment the monitoring system can sendinstructions to the condenser unit 101 to switch the compressor 105 to alow-speed mode to conserve power.

In one embodiment, the remote monitoring service knows theidentification codes or addresses of the data interface devices 955-957and correlates the identification codes with a database to determinewhether the refrigerant-cycle system is serving a relatively highpriority client such as, for example, a hospital, the home of an elderlyor invalid person, etc. In such circumstances, the remote monitoringsystem can provide relatively less cutback in cooling provided by therefrigerant-cycle system.

In one embodiment, the system 900 communicates with the monitoringsystem 950 to provide load shedding. Thus, for example, the monitoringsystem (e.g., a power company) can communicate with the data interfacedevice 956 and/or the data interface device 957 to turn off therefrigerant cycle system. The monitoring system 950 can thus rotate theon and off times of air conditioners across a region to reduce the powerload without implementing rolling blackouts. In one embodiment, the datainterface device 956 is configured as a retrofit device that can beinstalled in a condenser unit to provide remote shutdown. In oneembodiment, the data interface device 956 is configured as a retrofitdevice that can be installed in a condenser unit to remotely switch thecondenser-unit to a low power (e.g., energy conservation) mode. In oneembodiment, the data interface device 957 is configured as a retrofitdevice that can be installed in an evaporator unit to provide remoteshutdown or to remotely switch the system to a lower power mode. In oneembodiment, the remote system 950 sends separate shutdown and restartcommands to one or more of the data interface devices 955-957. In oneembodiment, the remote system 950 sends commands to the data interfacedevices 955-957 to shutdown for a specified period of time (e.g., 10min, 30 min, 1 hour, etc.) after which the system automaticallyrestarts.

In one embodiment, the system 900 communicates with the monitoringsystem 950 to control the temperature set point of the thermostat 952 toprevent blackouts or brownouts without regard to efficiency of therefrigerant-cycle system. When brownout or potential blackout conditionsoccur, the system 950 can override the homeowner's thermostat setting tocause the temperature set point on the thermostat 952 to change (e.g.increase) in order to reduce power usage. In most residentialinstallations, low-voltage control wiring is provided between thethermostat 952 and the evaporator unit 102 and condenser unit 101. Inmost residential (and many industrial) applications the thermostat 952receives electrical power via the low-voltage control wiring from astep-down transformer provided with the evaporator unit 102.

In one embodiment, the modem 955 is provided in connection with thepower meter 949, and the modem 955 communicates with the thermostat 952using wireless communications.

In a typical refrigeration or air conditioning system, the condenserunit 101 is placed outside the area being cooled and the evaporator unit102 is placed inside the area being cooled. The nature of outside andinside depend on the particular installation. For example, in an airconditioning or HVAC system, the condenser unit 101 is typically placedoutside the building, and the evaporator unit 102 is typically placedinside the building. In a refrigerator or freezer, the condenser unit101 is placed outside the refrigerator and the evaporator unit 102 isplaced inside the refrigerator. In any case, the waste heat from thecondenser should be dumped outside (e.g., away from) the area beingcooled.

When the system 900 is installed, the system 900 is programmed byspecifying the type of refrigerant used, and the characteristics of thecondenser 107, the compressor 105, and the evaporator unit 102. In oneembodiment, the system 900 is also programmed by specifying the size ofthe air handler system. In one embodiment, the system 900 is alsoprogrammed by specifying the expected (e.g., design) efficiency of thesystem 100.

The monitoring system can do a better job of monitoring efficiency thatpublished performance ratings such as the Energy Efficiency Ratio (EER)and SEER. The EER is determined by dividing the published steady statecapacity by the published steady sate power input at 80° F. dB/67° F. Wbindoor and 95° F. dB outdoor. This is objective yet unrealistic withrespect to system “real world” operating conditions. The published SEERrating of a system is determined by multiplying the steady state EERmeasured at conditions of 82° F. outdoor temperature, 80° F. dB/67° F.Wb indoor entering air temperature by the (run time) Part Load Factor(PLF) of the system. A major factor not considered in SEER calculationis the actual part loading factor of the indoor evaporator cooling coil,which reduces the unit's listed BTUH capacity and SEER efficiency level.Many older air handlers and duct systems, do not deliver the publishedBTUH and SEER Ratings. This is primarily due to inadequate air flowthrough the evaporator 110, a dirty evaporator 110, and/or dirty blowerwheels. Also, improper location of supply diffusers and return airregisters can result in inefficient floor level recirculation of thecold conditioned air, resulting in lack of heat loading of theevaporator 110.

By monitoring the system under actual load conditions, and by measuringthe relevant ambient temperature and humidity, the system 900 cancalculate the actual efficiency of the system 100 in operation.

FIG. 10 shows a monitoring system 1000 for monitoring the operation ofthe refrigerant-cycle system 100. The system 1000 shown in FIG. 10 isone example of an embodiment of the system 900 shown in FIGS. 9A-E. Inthe system 1000, a condenser unit sender 1002 monitors operation of thecondenser unit 101 through one or more sensors, a evaporator sender unit1003 monitors operation of the evaporator unit 102 through one or moresensors. The condenser unit sender 1002 and the sender unit 1003communicate with the thermostat 1001 to provide data to the buildingowner. For purposes of explanation, and not by way of limitation, inFIG. 10 the processor 904 and thermostat 952 from FIGS. 9A-E are shownas a single thermostat-processor. One of ordinary skill in the art willrecognize that the processor functions can be separated from thethermostat.

In one embodiment, a building interior temperature sensor 1009 isprovided to the thermostat 101. In one embodiment, a building interiorhumidity sensor 1010 is provided to the thermostat 101. In oneembodiment, the thermostat 1001 includes a display 1008 for displayingsystem status and efficiency. In one embodiment, the thermostat 1001includes a keypad 1050 and/or indicator lights (e.g., LEDs) 1051. Apower sensor 1011 to sense electrical power consumed by the compressor105 is provided to the condenser unit sender 1002. In one embodiment, apower sensor 1017 to sense electrical power consumed by the condenserfan 122 is provided to the condenser unit sender 1002. The air 125 fromthe evaporator 110 flows in the ductwork 1080.

In one embodiment, a temperature sensor 1012, configured to measure thetemperature of the refrigerant in the suction line 111 near thecompressor 105, is provided to the condenser unit sender 1002. In oneembodiment, a temperature sensor 1016, configured to measure thetemperature of the refrigerant in the hot gas line 106, is provided tothe condenser unit sender 1002. In one embodiment, a temperature sensor1014, configured to measure the temperature of the refrigerant in thefluid line 108 near the condenser 107, is provided to the condenser unitsender 1002.

Contaminants in the refrigerant lines 111, 106, 108, etc. can reduce theefficiency of the refrigerant-cycle system and can reduce the life ofthe compressor or other system components. In one embodiment, one ormore contaminant sensors 1034, configured to sense contaminants in therefrigerant (e.g., water, oxygen, nitrogen, air, improper oil, etc.) areprovided in at least one of the refrigerant lines and provided to thecondenser unit sender 1002 (or, optionally, to the evaporator unitsender 1003). In one embodiment, the contaminant sensor 1060 sensesrefrigerant fluid or droplets at the input to the compressor 105, whichcan cause damage to the compressor 105. In one embodiment, a contaminantsensor 1060 is provided in the liquid line 108 to sense bubbles in therefrigerant. Bubbles in the liquid line 106 may indicate low refrigerantlevels, an undersized condenser 109, insufficient cooling of thecondenser 109, etc. In one embodiment, the sensor 1034 senses water orwater vapor in the refrigerant lines. In one embodiment, the sensor 1034senses acid in the refrigerant lines. In one embodiment, the sensor 1034senses acid in the refrigerant lines. In one embodiment, the sensor 1034senses air or other gasses (e.g., oxygen, nitrogen, carbon dioxide,chlorine, etc.).

In one embodiment, a pressure sensor 1013, configured to measurepressure in the suction line 111, is provided to the condenser unitsender 1002. In one embodiment, a pressure sensor 1015, configured tomeasure pressure in the liquid line 108, is provided to the condenserunit sender 1002. In one embodiment, a pressure sensor (not shown),configured to measure pressure in the hot gas line 106, is provided tothe condenser unit sender 1002. In one embodiment, the pressure sensor1013 and the pressure sensor 1015 are connected to the system 100, byattaching the pressure sensors 1013 and 1015 to the service valves 120and 121, respectively. Attaching the pressure sensors to the pressurevalves is a convenient way to access refrigerant pressure in a retrofitinstallation without having to open the pressurized refrigerant system.

In one embodiment, a flow sensor 1031, configured to measure flow in thesuction line 111, is provided to the condenser unit sender 1002. In oneembodiment, a flow sensor 1030, configured to measure flow in the liquidline 108, is provided to the condenser unit sender 1002. In oneembodiment, a flow sensor (not shown), configured to measure flow in thehot gas line 106, is provided to the condenser unit sender 1002. In oneembodiment, the flow sensors are ultrasonic sensors that can be attachedto the refrigerant lines without opening the pressurized refrigerantsystem.

In one embodiment, a temperature sensor 1028 configured to measureambient temperature is provided to the condenser unit sender 1002. Inone embodiment, a humidity sensor 1029 configured to measure ambienthumidity is provided to the condenser unit sender 1002.

In one embodiment, a temperature sensor 1020, configured to measure thetemperature of the refrigerant in the liquid line 108 near theevaporator 110 is provided to the sender unit 1003. In one embodiment, atemperature sensor 1021, configured to measure the temperature of therefrigerant in the suction line 111 near the evaporator 110 is providedto the sender unit 1003.

In one embodiment, a temperature sensor 1026, configured to measure thetemperature of air 124 flowing into the evaporator 110 is provided tothe sender unit 1003.

In one embodiment, a temperature sensor 1026, configured to measure thetemperature of air 125 flowing out of the evaporator 110 is provided tothe sender unit 1003. In one embodiment, a flow sensor 1023, configuredto measure the airflow of air 125 flowing out of the evaporator 110 isprovided to the sender unit 1003. In one embodiment, a humidity sensor1024, configured to measure the temperature of air 125 flowing out ofthe evaporator 110 is provided to the sender unit 1003. In oneembodiment, a differential pressure sensor 1025, configured to measure apressure drop across the evaporator 110, is provided to the sender unit1003.

In one embodiment, the temperature sensors are attached to therefrigerant lines (e.g., the lines 106, 108, 111, in order to measurethe temperature of the refrigerant circulating inside the lines. In oneembodiment, the temperature sensors 1012 and/or 1016 are provided insidethe compressor 105. In one embodiment, the temperature sensors areprovided inside one or more of the refrigerant lines.

A tachometer 1033 senses rotational speed of the fan blades in the fan123. The tachometer is provided to the evaporator unit sender 1003. Atachometer 1032 senses rotational speed of the fan blades in thecondenser fan 122. The tachometer 1032 is provided to the condenser unitsender 1002.

In one embodiment, a power sensor 1027, configured to measure electricalpower consumed by the fan 123 is provided to the sender unit 1003.

In one embodiment, the sender unit 1003 communicates sensor data to thecondenser unit sender 1002 through wireless transmission. In oneembodiment, the sender unit 1003 communicates sensor data to thecondenser unit sender 1002 through existing HVAC wiring. In oneembodiment, the sender unit 1003 communicates sensor data to thecondenser unit sender 1002 through existing HVAC wiring by modulatingsensor data onto a carrier that is transmitted using the existing HVACwiring.

Each of the sensors shown in FIG. 10 (e.g., the sensors 1010-1034 etc.)are optional. The system 1000 can be configured with a subset of theillustrated sensors in order to reduce cost at the expense of monitoringsystem capability. Thus, for example, the contaminant sensors 1034 canbe eliminated, but ability of the system 1000 to detect the contaminantssensed by the sensor 1034 will be compromised or lost.

The pressure sensors 1013 and 1015 measure suction and dischargepressures, respectively, at the compressor 105. The temperature sensors1026 and 1022 measure evaporator 110 supply air and return air,respectively. The temperature sensors 1018 and 1019 measure input airand discharge air, respectively, at the condenser 107.

The power sensors 1011, 1017, and 1027 are configured to measureelectric power. In one embodiment, one or more of the power sensorsmeasure voltage provided to a load and power is computed by using aspecified impedance for the load. In one embodiment, one or more of thepower sensors measure current provided to a load and power is computedby using a specified impedance for the load. In one embodiment, one ormore of the power sensors measure voltage and current provided to a loadand power is computed by using a specified power factor for the load. Inone embodiment, the power sensors measure voltage, current, and thephase relationship between the voltage and the current.

The temperature sensors 1012 and/or 1021 measure the temperature of therefrigerant at the suction line 111. By measuring the suction line 111temperature, the superheat can be determined. The suction pressure hasbeen measured by the pressure sensor 1013, the evaporating temperaturecan be read from a pressure-temperature chart. The superheat is thedifference between the suction line 111 temperature and the evaporatingtemperature.

The temperature sensors 1014 and/or 1020 measure the temperature of therefrigerant in the liquid line 108. By measuring the liquid line 108temperature, the subcooling can be determined. The discharge pressure ismeasured by the pressure sensor 1015, and thus the condensingtemperature can be read from the pressure-temperature chart. Thesubcooling is the difference between the liquid line 108 temperature andthe condensing temperature.

In one embodiment, the system 1000 calculates efficiency by measuringthe work (cooling) done by the refrigerant-cycle system and dividing bythe power consumed by the system. In one embodiment, the system 1000monitors the system for abnormal operation. Thus, for example, in oneembodiment, the system 1000 measures the refrigerant temperature dropacross the condenser 109 using the temperature sensors 1016 and 1014 tobe used in calculating the heat removed by the condenser. The system1000 measures the refrigerant temperature drop across the evaporator 110to be used in calculating the heat absorbed by the evaporator 110.

The monitoring system is typically used to monitor the operation of asystem 100 that was originally checked out and put into proper operationcondition. Mechanical problems in an air conditioning system aregenerally classified in two categories: air side problems andrefrigeration side problems.

The primary problem that can occur in the air category is a reduction inairflow. Air handling systems do not suddenly increase in capacity, thatis, increase the amount of air across the coil. On the other hand, therefrigeration system does not suddenly increase in heat transferability. The system 1000 uses the temperature sensors 1026 and 1022 tomeasure the temperature drop of the air through the evaporator 110.After measuring the return air and supply air temperatures andsubtracting to get the temperature drop, the system 1000 checks to seewhether the temperature difference higher or lower than it should be.

FIG. 11 shows the temperature drop across in the air through theevaporator as a function of humidity. In one embodiment, the humiditysensors 1024 and/Or 1041 are used to measure building humidity, and/orthe humidity sensor 1041 is used to measure ambient humidity. Thehumidity readings are used to correct temperature readings for wet bulbtemperature according to relative humidity.

In one embodiment, a comparison of the desired (or expected) temperaturedrop across the evaporator 110 with the measured actual temperaturedrop, is used to help classify potential air problems fromrefrigerant-cycle problems. If the actual temperature drop is less thanthe required temperature drop, then the airflow has likely been reduced.Reduced airflow can be caused by dirty air filters or evaporator 110,problems with the fan 123, and/or unusual restrictions in the ductsystem.

Air filters of the throwaway type are typically replaced at least twiceeach year, at the beginning of both the cooling and heating seasons. Inone embodiment, the thermostat allows the owner to indicate when a newair filter is installed. The thermostat keeps track of the time thefilter has been in use, and provides a reminder to the owner when thefilter should be replaced. In one embodiment, the thermostat uses actualelapsed clock time to determine filter usage.

In one embodiment, the thermostat 1001 calculates filter usage accordingto the amount of time the air handler has been blowing air through thefilter. Thus, for example, in moderate climates or seasons where the airhandler system is not used continuously, the thermostat will wait alonger period of actual time before indicating that filter replacementis warranted. In some areas of higher use or where dust is high, thefilter will generally have to be replaced relatively more often. In oneembodiment, the thermostat uses a weighting factor to combine runningtime with idle time to determine filter usage. Thus, for example, indetermining filter usage, hours when the hair handler is blowing airthorough the filter are weighted relatively more heavily than hourswhere the air handler system is idle. In one embodiment, the owner canprogram the thermostat to indicate that filter replacement is neededafter a specified number of hours or days (e.g., as actual days, asrunning days, or as a combination thereof).

In one embodiment, the thermostat 1001 is configured to receiveinformation from an information source regarding daily atmospheric dustconditions and to use such information in calculating filter usage.Thus, in one embodiment, when calculating filter use, the thermostatweighs days of relatively high atmospheric dust relatively more heavilythan days of relatively low atmospheric dust. In one embodiment, theinformation source for atmospheric dust information includes a datanetwork, such as, for example, the Internet, a pager network, a localarea network, etc.

In one embodiment, the thermostat collects data for calculating filterusage and passes such data to a computer monitoring system.

In commercial and industrial applications, a regular schedule ofmaintenance is generally used. In one embodiment, sensors are providedin connection with the air filter, as described below in connection withFIG. 11.

In one embodiment, power measured by the power meter 1027 is used tohelp diagnose and detect problems with the blower 123 and/or the airhandler system. If the blower 123 is drawing too much or too littlecurrent, or if the blower 123 is showing a low power factor, thenpossible problems with the blower and/or air handler system areindicated.

Placing furniture or carpeting over return air grilles reduces the airavailable for the blower to handle. Shutting off the air to unused areaswill reduce the air over the evaporator 110. Covering a return airgrille to reduce the noise from the centrally located furnace or airhandler may reduce the objectionable noise, but it also drasticallyaffects the operation of the system by reducing the air quantity. Thecollapse of the return air duct system will affect the entire ductsystem performance. Air leaks in the return duct will raise the returnair temperature and reduce the temperature drop across the coil.

The air flow sensor 1023 can be used to measure air flow through theducts. In one embodiment, the air flow sensor 1023 is a hot wire (or hotfilm) mass flow sensor. In one embodiment, the differential pressuresensor 1025 is used to measure airflow through the evaporator 110. Inone embodiment, the differential pressure sensor 1025 is used to measuredrop across the evaporator 110. In one embodiment, the pressure dropacross the evaporator is used to estimate when the evaporator 110 isrestricting airflow (e.g., due to damage, dirt, hair, dust, etc.). Inone embodiment, the differential pressure sensor 1025 is used to measuredrop across an air filter to estimate when the filter is restrictingairflow (e.g., due to age, damage, dirt, hair, dust, etc.). In oneembodiment, the indicator lights 1051 are used to indicate that thefilter needs to be changed. In one embodiment, the indicator lights 1051are used to indicate that the evaporator 110 needs to be cleaned.

In one embodiment, the airflow sensor 1023 is used to measure airflowinto the ductwork 1080. In one embodiment, the indicator lights 1051 areused to indicate that the airflow into the ductwork 1080 is restricted(e.g., due to dirt, furniture or carpets placed in front of vents,closed vents, dirty evaporator, dirty fan blades, etc.).

In one embodiment, a dust sensor is provided in the air stream of theevaporator 110. In one embodiment, the dust sensor includes a lightsource (optical and/or infrared) and a light sensor. The dust sensormeasures light transmission between the source and the light sensor. Thebuildup of dust will cause the light to be attenuated. The sensordetects the presence of dust buildup at the evaporator 110 by measuringlight attenuation between the light source and the light sensor. Whenthe attenuation exceeds a desired value, the monitoring system 1000indicates that cleaning of the air flow system is needed (e.g., the fan123, the duct work 1080, and/or the evaporator 110, etc.).

In one embodiment, the power sensor 1027 is used to measure powerprovided to the blower motor in the fan 123. If the fan 123 is drawingtoo much power or too little power, then potential airflow problems areindicated (e.g., blocked or closed vents, dirty fan blades, dirtyevaporator, dirty filter, broken fan belt, slipping fan belt, etc.).

If the temperature drop across the evaporator 1010 is less than desired,then the heat removal capacity of the system has been reduced. Suchproblems can generally be divided into two categories: refrigerantquantity, and refrigerant flow rate. If the system 100 has the correctamount of refrigerant charge and refrigerant is flowing at the desiredrate (e.g., as measured by the flow sensors 1031 and/or 1030), thesystem should work efficiently and deliver rated capacity. Problems withrefrigerant quantity or flow rate typically affect the temperatures andpressures that occur in the refrigerant-cycle system when the correctamount of air is supplied through the evaporator 110. If the system isempty of refrigerant, a leak has occurred, and it must be found andrepaired. If the system will not operate at all, it is probably anelectrical problem that must be found and corrected.

If the system 100 will start and run but does not produce satisfactorycooling, then the amount of heat picked up in the evaporator 110 plusthe amount of motor heat added and the total rejected from the condenser107 is not the total heat quantity the unit is designed to handle. Todiagnose the problem, the information listed in Table 1 is used. Theseresults compared to normal operating results will generally identify theproblem: (1) Evaporator 110 operating temperature; (2) Condensing unitcondensing temperature; and/or (3) Refrigerant subcooling.

These items can be modified according to the expected energy efficiencyratio (EER) of the unit. The amount of evaporation and condensingsurface designed into the unit are the main factors in the efficiencyrating. A larger condensing surface results in a lower condensingtemperature and a higher EER. A larger evaporating surface results in ahigher suction pressure and a higher EER. The energy efficiency ratiofor the conditions is calculated by dividing the net capacity of theunit in Btu/hr by the watts input.

TABLE 1 Condenser Suction Evaporator Hot Gas Liquid Compressor PressureSuperheat Pressure Subcooling Current Probable Cause (psig) (° F.)(psig) (° F.) (A) 1. Insufficient or Low Low Low Normal Low unbalancedload 2. Excessive load High High High Normal High 3. Low ambient LowHigh Low Normal Low temperature 4. High ambient High High High NormalHigh temperature 5. Refrigerant undercharge Low High Low Low Low 6.Refrigerant overcharge High Low High High High 7. Liquid linerestriction Low High Low High Low 8. Plugged capillary tube Low HighHigh High Low 9. Suction line restriction Low High Low Normal Low 10.Hot gas line restriction High High High Normal High 11. Inefficientcompressor High High Low Low Low

Normal evaporator 110 operating temperatures can be found by subtractingthe design coil split from the average air temperature going through theevaporator 110. The coil split will vary with the system design. Systemsin the EER range of 7.0 to 8.0 typically have design splits in the range25 to 30° F. Systems in the EER range of 8.0 to 9.0 typically havedesign splits in the range 20 to 25° F. Systems with 9.0+EER ratingswill have design splits in the range 15 to 20° F. The formula used fordetermining coil operating temperatures is:

${{COT} = {\left( \frac{{EAT} + {LAT}}{2} \right) - {split}}}\mspace{11mu}$where COT is the coil operating temperature, EAT is the entering airtemperature of the coil (e.g., as measured by the temperature sensor1026), LAT is the leaving air temperature of the coil (e.g., as measuredby the temperature sensor 1022), and split is the design splittemperature.

The value (EAT+LAT)/2 is the average air temperature, which is alsoreferred to as the mean temperature difference (MTD). It is alsosometimes referred to as the coil TED or ΔT.

“Split” is the design split according to the EER rating. For example, aunit having an entering air condition of 80° DB and a 20° F. temperaturedrop across the evaporator 110 coil will have an operating coiltemperature determined as follows: For an EER rating of 7.0 of 8.0:

${COT} = {{\left( \frac{80 + 60}{2} \right) - {25\mspace{14mu}{to}\mspace{14mu} 30^{\circ}}} = {40\mspace{14mu}{to}\mspace{14mu} 45^{\circ \mspace{14mu}}{F.}}}$For an EER rating of 8.0 to 9.0:

${COT} = {{\left( \frac{80 + 60}{2} \right) - {20\mspace{14mu}{to}\mspace{14mu} 25^{\circ}}} = {45\mspace{14mu}{to}\mspace{14mu} 50^{\circ}\mspace{14mu}{F.}}}$For an EER rating of 9.0+:

${COT} = {{\left( \frac{80 + 60}{2} \right) - {15\mspace{14mu}{to}\mspace{14mu} 20^{\circ}}} = {50\mspace{14mu}{to}\mspace{14mu} 55^{\circ}\mspace{14mu}{F.}}}$Thus, the operating coil temperature changes with the EER rating of theunit.

The surface area of the condenser 107 affects the condensing temperaturethe system 100 must develop to operate at rated capacity. The variationin the size of the condenser 107 also affects the production cost andprice of the unit. The smaller the condenser 107, the lower theefficiency (EER) rating. In the same EER ratings used for the evaporator110, at 95° F. outside ambient, the 7.0 to 8.0 EER category will operatein the 25 to 30° condenser 107 split range, the 8.0 to 9.0 EER categoryin the 20 to 25° condenser 107 split range, and the 9.0+ EER category inthe 20 to 25° condenser 107 split range, and the 9.0+ EER category inthe 15 to 20° condenser 107 split range.

This means that when the air entering the condenser 107 is at 95° F.,the formula for finding the condensing temperature is:RCT=EAT+splitwhere RCT is the refrigerant condensing temperature, EAT is the enteringair temperature of the condenser 107, and split is the designtemperature difference between the entering air temperature and thecondensing temperatures of the hot high pressure vapor from thecompressor 105.

For example, using the formula with 95° F. EAT, the split for thevarious EER systems would be:

For an EER rating of 7.0 to 8.0RCT=95°+25 to 30°=120 to 125° F.

For an EER rating of 8.0 to 9.0RCT=95°+20 to 25°=115 to 120° F.

For an EER rating of 9.0+RCT=95°+15 to 20°=110 to 115° F.

The operating head pressures vary not only from changes in outdoortemperatures but with the different EER ratings.

The amount of subcooling produced in the condenser 107 is determinedprimarily by the quantity of refrigerant in the system. The temperatureof the air entering the condenser 107 and the load in the evaporator 110will have only a relatively small effect on the amount of subcoolingproduced. The amount of refrigerant in the system has the predominanteffect. Therefore, regardless of EER ratings, the unit should have, ifproperly charged, a liquid subcooled to 15 to 20° F. High ambienttemperatures will produce the lower subcooled liquid because of thereduced quantity of refrigerant in the liquid state in the system. Morerefrigerant will stay in the vapor state to produce the higher pressureand condensing temperatures needed to eject the required amount of heat.

Table 1 shows 11 probable causes of trouble in an air conditioningsystem. After each probable cause is the reaction that the cause wouldhave on the refrigeration system low side or suction pressure, theevaporator 110 superheat, the high side or discharge pressure, theamount of subcooling of the liquid leaving the condenser 107, and theamperage draw of the condensing unit. In one embodiment, an airflowsensor (not shown) is included to measure the air over the condenser.

Insufficient air over the evaporator 110 (as measured, for example, byusing the airflow sensor 1023 and/or the differential pressure sensor1025) is indicated by a greater than desired temperature drop in the airthrough the evaporator 110. An unbalanced load on the evaporator 110will also give the opposite indication, indicating that some of thecircuits of the evaporator 110 are overloaded while others are lightlyloaded. In one embodiment, the temperature sensor 1022 includes multiplesensors to measure the temperature across the evaporator. The lightlyloaded sections of the evaporator 110 allow liquid refrigerant to leavethe coil and enter the suction manifold and suction line.

In TXV systems, the liquid refrigerant passing the sensing bulb of theTXV can cause the valve to close down. This reduces the operatingtemperature and capacity of the evaporator 110 as well as lowering thesuction pressure. The evaporator 110 operating superheat can become verylow because of the liquid leaving some of the sections of the evaporator110.

With inadequate airflow, high side or discharge pressure will be low dueto the reduced load on the compressor 105, reduced amount of refrigerantvapor pumped, and reduced heat load on the condenser 107. Condenser 107liquid subcooling would be on the high side of the normal range becauseof the reduction in refrigerant demand by the TXV. Condensing unitamperage draw would be down due to the reduced load.

In systems using fixed metering devices, the unbalanced load wouldproduce a lower temperature drop of the air through the evaporator 110because the amount of refrigerant supplied by the fixed metering devicewould not be reduced; therefore, the system pressure (boiling point)would be approximately the same.

The evaporator 110 superheat would drop to zero with liquid refrigerantflooding into the suction line. Under extreme case of imbalance, liquidreturning to the compressor 105 could cause damage to the compressor105. The reduction in heat gathered in the evaporator 110 and thelowering of the refrigerant vapor to the compressor 105 will lower theload on the compressor 105. The compressor 105 discharge pressure (hotgas pressure) will be reduced.

The flow rate of the refrigerant will be only slightly reduced becauseof the lower head pressure. The subcooling of the refrigerant will be inthe normal range. The amperage draw of the condensing unit will beslightly lower because of the reduced load on the compressor 105 andreduction in head pressure.

In the case of excessive load, the opposite effect exists. Thetemperature drop of the air through the coli will be less, because theunit cannot cool the air as much as it should. Air is moving through thecoil at too high a velocity. There is also the possibility that thetemperature of the air entering the coil is higher than the return airfrom the conditioned area. This could be from air leaks in the returnduct system drawing hot air from unconditioned areas.

The excessive load raises the suction pressure. The refrigerant isevaporating at a rate faster than the pumping rate of the compressor105. If the system uses a TXV, the superheat will be normal to slightlyhigh. The valve will operate at a higher flow rate to attempt tomaintain superheat settings. If the system uses fixed metering devices,the superheat will be high. The fixed metering devices cannot feedenough increase in refrigerant quantity to keep the evaporator 110 fullyactive.

The high side or discharge pressure will be high. The compressor 105will pump more vapor because of the increase in suction pressure. Thecondenser 107 must handle more heat and will develop a higher condensingtemperature to eject the additional heat. A higher condensingtemperature means a greater high side pressure. The quantity of liquidin the system has not changed, nor is the refrigerant flow restricted.The liquid subcooling will be in the normal range. The amperage draw ofthe unit will be high because of the additional load on the compressor105.

When the temperature of the ambient air entering the condenser 107 islow, then the condenser 107 heat transfer rate is excessive, producingan excessively low discharge pressure. As a result, the suction pressurewill be low because the amount of refrigerant through the meteringdevice will be reduced. This reduction will reduce the amount of liquidrefrigerant supplied to the evaporator 110. The coil will produce lessvapor and the suction pressure drops.

The decrease in the refrigerant flow rate into the coil reduces theamount of active coil, and a higher superheat results. In addition, thereduced system capacity will decrease the amount of heat removed fromthe air. There will be higher temperature and relative humidity in theconditioned area and the high side pressure will be low. This starts areduction in system capacity. The amount of subcooling of the liquidwill be in the normal range. The quantity of liquid in the condenser 107will be higher, but the heat transfer rate of the evaporator 110 isless. The amperage draw of the condensing unit will be less because thecompressor 105 is doing less work.

The amount of drop in the condenser 107 ambient air temperature that theair conditioning system will tolerate depends on the type of pressurereducing device in the system. Systems using fixed metering devices willhave a gradual reduction in capacity as the outside ambient drops from95° F. This gradual reduction occurs down to 65° F. Below thistemperature the capacity loss is drastic, and some means of maintaininghead pressure must be employed to prevent the evaporator 110 temperaturefrom dropping below freezing. Some systems control air through thecondenser 107 via dampers in the airstream or a variable speed condenser107 fan.

Systems that use TXV will maintain higher capacity down to an ambienttemperature of 47° F. Below this temperature, controls must be used. Thecontrol of airflow through the condenser 107 using dampers or thecondenser 107 fan speed control can also be used. In larger TXV systems,liquid quantity in the condenser 107 is used to control head pressure.

The higher the temperature of the air entering the condenser 107, thehigher the condensing temperature of the refrigerant vapor to eject theheat in the vapor. The higher the condensing temperature, the higher thehead pressure. The suction pressure will be high for two reasons: (1)the pumping efficiency of the compressor 105 will be less; and (2) thehigher temperature of the liquid will increase the amount of flash gasin the metering device, further reducing the system efficiency.

The amount of superheat produced in the coil will be different in a TXVsystem and a fixed metering device system. In the TXV system the valvewill maintain superheat close to the limits of its adjustment range eventhough the actual temperatures involved will be higher. In a fixedmetering device system, the amount of superheat produced in the coil isthe reverse of the temperature of the air through the condenser 107. Theflow rate through the fixed metering devices are directly affected bythe head pressure. The higher the air temperature, the higher the headpressure and the higher the flow rate. As a result of the higher flowrate, the subcooling is lower.

Table 2 shows the superheat that will be developed in a properly chargedair conditioning system using fixed metering devices. The head pressurewill be high at the higher ambient temperatures because of the highercondensing temperatures required. The condenser 107 liquid subcoolingwill be in the lower portion of the normal range. The amount of liquidrefrigerant in the condenser 107 will be reduced slightly because morewill stay in the vapor state to produce the higher pressure andcondensing temperature. The amperage draw of the condensing unit will behigh.

TABLE 2 Air Temperature Entering Condenser 107 Superheat (° F.) ° F. 6530 75 25 80 20 85 18 90 15 95 10 105 & above 5

A shortage of refrigerant in the system means less liquid refrigerant inthe evaporator 110 to pick up heat, and lower suction pressure. Thesmaller quantity of liquid supplied the evaporator 110 means less activesurface in the coil for vaporizing the liquid refrigerant, and moresurface to raise vapor temperature. The superheat will be high. Therewill be less vapor for the compressor 105 to handle and less head forthe condenser 107 to reject, lower high side pressure, and lowercondensing temperature. The compressor 105 in an air conditioning systemis cooled primarily by the cool returning suction gas. Compressor 105 sthat are low on charge can have a much higher operating temperature.

The amount of subcooling will be below normal to none, depending on theamount of undercharge. The system operation is usually not affected veryseriously until the subcooling is zero and hot gas starts to leave thecondenser 107, together with the liquid refrigerant. The amperage drawof the condensing unit will be slightly less than normal.

An overcharge of refrigerant will affect the system in different ways,depending on the pressure reducing device used in the system and theamount of overcharge.

In system using a TXV, the valve will attempt to control the refrigerantflow in the coil to maintain the superheat setting of the valve.However, the extra refrigerant will back up into the condensing 107,occupying some of the heat transfer area that would otherwise beavailable for condensing. As a result, the discharge pressure will beslightly higher than normal, the liquid subcooling will be high, and theunit amperage draw will be high. The suction pressure and evaporator 110superheat will be normal. Excessive overcharging will cause even higherhead pressure, and hunting of the TXV.

For TXV systems with excessive overcharge the suction pressure willtypically be high. Not only does the reduction in compressor 105capacity (due to higher head pressure) raise the suction pressure, butthe higher pressure will cause the TXV valve to overfeed on its openingstroke. This will cause a wider range of hunting of the valve. Theevaporator 110 superheat will be very erratic from the low normal rangeto liquid out of the coil. The high side or discharge pressure will beextremely high. Subcooling of the liquid will also be high because ofthe excessive liquid in the condenser 107. The condensing unit amperagedraw will be higher because of the extreme load on the compressor 105motor.

The amount of refrigerant in the fixed metering system has a directeffect on system performance. An overcharge has a greater effect than anundercharge, but both affect system performance, efficiency (EER), andoperating cost.

FIGS. 12 through 14 show how the performance of a typical capillary tubeair conditioning system is affected by an incorrect amount ofrefrigerant charge. In FIG. 12, at 100% of correct charge (55 oz), theunit develops a net capacity of 26,200 Btu/hr. When the amount of chargeis varied 5% in either direction, the capacity drops as the chargevaried. Removing 5% (3 oz) of refrigerant reduces the net capacity to25,000 Btu/hr. Another 5% (2.5 oz) reduces the capacity to 22,000Btu/hr. From there on the reduction in capacity became very drastic: 85%(8 oz), 18,000 Btu/hr; 80% (11 oz), 13,000 Btu/hr; and 75% (14 oz), 8000Btu/hr.

Overcharge has a similar effect but at a greater reduction rate. Theaddition of 3 oz of refrigerant (5%) reduces the net capacity to 24,600Btu/hr; 6 oz added (10%) reduces the capacity to 19,000 Btu/hr; and 8 ozadded (15%) drops the capacity to 11,000 Btu/hr. This shows thatovercharging of a unit has a greater effect per ounce of refrigerantthan does undercharging.

FIG. 13 is a chart showing the amount of electrical energy the unitdemand because of pressure created by the amount of refrigerant in thesystem as the refrigerant charge is varied. At 100% of charge (55 oz)the unit uses 32 kW. As the charge is reduced, the wattage demand alsodrops, to 29.6 kW at 95% (3 oz), to 27.6 kW at 90% (6.5 oz), to 25.7 kWat 85% (8 oz), to 25 kW at 80% (11 oz), and to 22.4 kW at 75% (14 ozshort of correct charge). When the unit is overcharged, the powerconsumed also increases. At 3 oz (5% overcharge) the power consumed is34.2 kW, at 6 oz (10% overcharge) 39.5 kW, and at 8 oz (15% overcharge),48 kW.

FIG. 14 shows the efficiency of the unit (EER rating) based on theBtu/hr capacity of the system versus the power consumed by thecondensing unit. At correct charge (55 oz) the efficiency (EER rating)of the unit is 8.49. As the refrigerant is reduced, the EER rating dropsto 8.22 at 9% of charge, to 7.97 at 90%, to 7.03 at 85%, to 5.2 at 80%,and to 3.57 at 75% of full refrigerant charge. When refrigerant isadded, at 5% (3 oz) the EER rating drops to 7.19. At 10% (6 oz) the EERis 4.8, and at 15% overcharge (8 oz) the EER is 2.29.

The effect of overcharge produces a high suction pressure because therefrigerant flow to the evaporator 110 increases. Suction superheatdecreases because of the additional quantity to the evaporator 110. Atapproximately 8 to 10% of overcharge, the suction superheat becomes zeroand liquid refrigerant will leave the evaporator 110. This causesflooding of the compressor 105 and greatly increases the chance ofcompressor 105 failure. The high side or discharge pressure is highbecause of the extra refrigerant in the condenser 107. Liquid subcoolingis also high for the same reason. The power draw increases due to thegreater amount of vapor pumped as well as the higher compressor 105discharge pressure.

Restrictions in the liquid line 108 reduce the amount of refrigerant tothe pressure reducing device 109. Both TXV valve systems and fixedmetering device systems will then operate with reduced refrigerant flowrate to the evaporator 110. The following observations can be made ofliquid line 108 restrictions. First, the suction pressure will be lowbecause of the reduced amount of refrigerant to the evaporator 110. Thesuction superheat will be high because of the reduced active portion ofthe coil, allowing more coil surface for increasing the vaportemperature as well as reducing the refrigerant boiling point. The highside or discharge pressure will be low because of the reduced load onthe compressor 105. Liquid subcooling will be high. The liquidrefrigerant will accumulate in the condenser 107. It cannot flow out atthe proper rate because of the restriction. As a result, the liquid willcool more than desired. Finally, the amperage draw of the condensingunit will be low.

Either a plugged fixed metering device or plugged feeder tube betweenthe TXV valve distributor and the coil will cause part of the coil to beinactive. The system will then be operating with an undersized coil,resulting in low suction pressure because the coil capacity has beenreduced. The suction superheat will be high in the fixed metering devicesystems. The reduced amount of vapor produced in the coil and resultantreduction in suction pressure will reduce compressor 105 capacity, headpressure, and the flow rate of the remaining active capillary tubes. Thehigh side or discharge pressure will be low.

Liquid subcooling will be high; the liquid refrigerant will accumulatein the condenser 107. The unit amperage draw will be low.

In TXV systems, a plugged feeder tube reduces the capacity of the coil.The coil cannot provide enough vapor to satisfy the pumping capacity ofthe compressor 105 and the suction pressure balances out at a lowpressure. The superheat, however, will be in the normal range becausethe valve will adjust to the lower operating conditions and maintain thesetting superheat range. The high side or discharge pressure will be lowbecause of the reduced load on the compressor 105 and condenser 107.

Low suction and discharge pressure indicate a refrigerant shortage. Theliquid subcooling is normal to slightly above normal. This indicates asurplus of refrigerant in the condenser 107. Most of the refrigerant isin the coil, where the evaporation rate is low due to the higheroperating pressure in the coil. The amperage draw of the condensing unitwould be low because of the light load on the compressor 105.

If the hot gas line 106 is restricted, then the high side or compressor105 discharge pressure will be high if measured at the compressor 105outlet or low if measured at the condenser 107 outlet or liquid line. Ineither case, the compressor 105 current draw will be high. The suctionpressure is high due to reduced pumping capacity of the compressor 105.The evaporator 110 superheat is high because the suction pressure ishigh. The high side pressure is high when measured at the compressor 105discharge or low when measured at the liquid line. Liquid subcooling isin the high end of the normal range. Even with all of this, thecompressor 105 amperage draw is above normal. All symptoms point to anextreme restriction in the hot gas line 106. This problem is easilyfound when the discharge pressure is measured at the compressor 105discharge.

When the measuring point is the liquid line 108 at the condenser 107outlet, the facts are easily misinterpreted. High suction pressure andlow discharge pressure will usually be interpreted as an inefficientcompressor 105. The amperage draw of the compressor 105 must bemeasured. The high amperage draw indicates that the compressor 105 isoperating against a high discharge pressure. A restriction apparentlyexists between the outlet of the compressor 105 and the pressuremeasuring point.

When the compressor 105 will not pump the required amount of refrigerantvapor (e.g., because it is undersized, or is not working at ratedcapacity). The suction pressure will balance out higher than normal. Theevaporator 110 superheat will be high. The high side or dischargepressure will be extremely low. Liquid subcooling will be low becausenot much heat will be in the condenser 107. The condensing temperaturewill therefore be close to the entering air temperature. The amperagedraw of the condensing unit will be extremely low, indicating that thecompressor 105 is doing very little work.

The following formulas can be used by the systems 900, 1000 to calculatevarious operating parameters of the refrigerant-cycle system 100 usingdata from one or more of the sensors shown in FIG. 10.

Power is:Watts=volts×amps×PFwhere PF is the power factor.

Heat is:Btu=W×ΔT

Specific heat is:Btu=W×c×ΔT

Sensible heat added or removed from a substance is:Q=W×SH×ΔT

Latent heat added or removed from a substance is:Q=W×LH

The refrigeration effect is:

$W = \frac{200}{NRE}$where W weight of refrigerant circulated per minute (e.g., lb/min), 200Btu/min is the equivalent of 1 ton of refrigeration, and NRE is the netrefrigerating effect (Btu/lb of refrigerant)

The coefficient of performance (COP) is:

${COP} = \frac{refrigerating\_ effect}{{heat\_ of}{\_ compression}}$

System capacity is:Q _(t)=4.45×CFM×Δhwhere Q_(t) is the total (sensible and latent) cooling being done, CFMis the airflow across the evaporator 110, and Δh is the change ofenthalpy of the air across the coil

Condensing temperature is:RCT=EAT+splitwhere RCT is the refrigerant condensing temperature, EAT is thetemperature of the air entering the condenser 107, and split is thedesign temperature difference between the entering air temperature andthe condensing temperatures of the hot high-pressure vapor from thecompressor 105

Net cooling capacity is:HC=HT−HMwhere HT is the heat transfer (gross capacity), HM is the motor heat, HCis the net cooling capacity, and PF is the power factor.

Airflow rate of a system can be expressed as:Q=Q _(s)(1.08×TD)where Q is the flow rate in CFM, Q_(s) is the sensible-heat load inBut/hr, and TD is the dry bulb temperature difference in ° F.

In a fan, airflow (CFM) is approximately related to rotation (rpm) asfollows:

$\frac{{CFM}_{2}}{{CFM}_{1}} = \frac{{rpm}_{2}}{{rpm}_{1}}$

In a fan, pressure is approximately related to rotation as follows:

$\frac{{SP}_{2}}{{SP}_{1}} = \left( \;\frac{{rpm}_{2}}{{rpm}_{1}} \right)^{2}$

In a fan, work is approximately related to rotation as follows:

$\frac{{Bhp}_{2}}{{Bhp}_{1}} = \left( \;\frac{{rpm}_{2}}{{rpm}_{1}} \right)^{3}$

In one embodiment, the tachometer 1033 is provided to measure therotational velocity of the fan 123. In one embodiment, the tachometer1032 is provided to measure the rotational velocity of the fan 122. Inone embodiment, the system 1000 uses one or more of the above fanequations to calculate desired fan rotation rates. In one embodiment,the system 1000 controls the speed of the fan 123 and/or the fan 122 toincrease system efficiency.

The quantity of air used for cooling, based on the sensible cooling isapproximately:CFM=H _(s)/(TD×1.08)

The sensible heat removed isQ _(s)=1.08×CFM×DBT difference

The latent heat removed is:Q _(t)=0.68×CFM×gr moisture difference

The total heat removed is:Q _(t)=Q_(s) +Q ₁orQ _(t)=4.5×CFM×total heat difference

The rate of heat transfer is:Q _(t) =U×A×TDwhere Q is the heat transfer (Btuh), U is the overall heat transfercoefficient (Btuh/Ft²/° F.), A is the area (ft²), TD is the temperaturedifference between inside and outside design temperature and therefrigerated space design temperature.

The keypad 1050 is used to provide control inputs to the efficiencymonitoring system. The display 1008 provides feedback to the user,temperature set point display. In one embodiment, the power use and/orpower cost can be displayed on the display 1008. In one embodiment, thesystem 1000 receives rate information from the power company to use incalculating power costs. In one embodiment, the absolute efficiency ofthe refrigerant-cycle system can be shown on the display 1008. In oneembodiment, the relative efficiency of the refrigerant-cycle system canbe shown on the display 1008. In one embodiment, the data from varioussensors in the system 1000 can be shown on the display 1008. In oneembodiment, diagnostic messages (e.g., change the filter, addrefrigerant, etc.) are shown on the display 1008. In one embodiment,messages from the power company are shown on the display 1008. In oneembodiment, warning messages from the power company are shown on thedisplay 1008. In one embodiment, the thermostat 1001 communicates withthe power company (or other remote device) using power linecommunication methods such as, for example, BPL.

Then the system 1000 is configured, the installer programs in the fixedsystem parameters needed for calculation of efficiency and/or otherquantities derived from the sensor data. Typical fixed programmedparameters include the type of refrigerant, the compressorspecifications, the condenser specifications, the evaporatorspecifications, the duct specifications, the fan specifications, thesystem SEER, and/or other system parameters. Typical fixed programmedparameters can also include equipment model and/or serial numbers,manufacturer data, engineering data, etc.

In one embodiment, the system 1000 is configured by bringing therefrigerant-cycle system up to design specifications, and then runningthe system 1000 in a calibration mode wherein the system 1000 takessensor readings to measure normal baseline parameters for therefrigerant-cycle system. Using the measured baseline data, the system1000 can calculate various system parameters (e.g., split temperatures,etc.).

In one embodiment, the system 1000 is first run in a calibration mode tomeasure baseline data, and then run in a normal monitoring mode whereinit compares operation of the refrigerant-cycle system with the baselinedata. The system 1000 then gives alerts to potential problems when theoperating parameters vary too much from the baseline data.

In one embodiment, the system 1000 is configured by using a combinationof programmed parameters (e.g., refrigerant type, temperature splits,etc.) and baseline data obtained by operating the refrigerant-cyclesystem.

FIG. 15 shows a differential-pressure sensor 1502 used to monitor an airfilter 1501 in an air-handler system. As the filter becomes clogged, thedifferential pressure across the filter will rise. This increase indifferential pressure is measured by the differential pressure sensor1502. The differential pressure measured by the differential pressuresensor 1502 is used to assess the state of the filter 1501. When thedifferential pressure is too high, then replacement of the filter 1501is indicated.

FIG. 16 shows the differential-pressure sensor 1502 from FIG. 15provided to a wireless communication unit to allow the data from thedifferential pressure sensor 1502 to be provided to other aspects of themonitoring system, such as, for example, the condenser unit sender 1002or the thermostat 1001.

FIG. 17 shows the system of FIG. 16 implemented using a filter frame1701 to facilitate retrofitting of existing air handler systems. Theframe 1701 includes the sensor 1502 and the sender 1601. The frame 1701is configured to fit into a standard filter frame. The frame 1701 isconfigured to hold a standard filter 1501. In one embodiment, the frame1701 evaluates the cleanliness of the filter 1501 by measuring adifferential pressure between the filter input and output air. In oneembodiment, the frame 1701 evaluates the cleanliness of the filter 1501by providing a source of light on one side of the filter, a light sensoron the other side of the filter, and by measuring the light transmissionthrough the filter. In one embodiment, the frame 1701 is calibrated to abaseline light transmission level. In one embodiment, the frame 1701signals that the filter is dirty when the light transmission falls belowa fixed threshold level. In one embodiment, the frame 1701 calibrates abaseline light transmission level each time a clean, filter isinstalled. In one embodiment, the frame 1701 signals that the filter isdirty when the light transmission falls below a percentage of thebaseline level.

Although various embodiments have been described above, otherembodiments will be within the skill of one of ordinary skill in theart. Thus, for example, although described primarily in terms of anair-conditioning system, one of ordinary skill in the art will recognizethat all or part of the system 1000 can be applied to otherrefrigerant-cycle systems, such as, for example, commercial HVACsystems, refrigerator systems, freezers, water chillers, etc. Thus, theinvention is limited only by the claims that follow.

1. An intelligent thermostat for monitoring the operation of arefrigerant-cycle system, comprising: a display configured to displaytemperature and system efficiency; and a processing system configured toreceive sensor data from one or more condenser unit sensors and one ormore evaporator unit sensors, said processing system configured tocalculate an efficiency of said refrigerant-cycle system using at leasta portion of said sensor data from said one or more condenser unitsensors and at least a portion of said sensor data from said one or moreevaporator unit sensors, and to display a parameter related to saidefficiency, wherein said processing system is configured to diagnoseperformance problems due to excessive load using at least a portion ofsaid sensor data from said one or more condenser unit sensors and atleast a portion of said sensor data from said one or more evaporatorunit sensors, wherein said efficiency comprises an actual efficiencybased at least in part on an ambient temperature.
 2. The intelligentthermostat of claim 1, wherein said processing system is configured tocalculate and display an energy cost of using said refrigerant-cyclesystem.
 3. The intelligent thermostat of claim 1, wherein saidprocessing system is configured to calculate and display energy usage ofsaid refrigerant-cycle system.
 4. The intelligent thermostat of claim 1,wherein said processing system is configured to diagnose performanceproblems due to refrigerant overcharge.
 5. The intelligent thermostat ofclaim 1, wherein said processing system is configured to diagnoseperformance problems due to liquid line restriction.
 6. The intelligentthermostat of claim 1, wherein said processing system is configured toidentify performance problems due to suction line restriction.
 7. Theintelligent thermostat of claim 1, wherein said processing system isconfigured to identify performance problems due to hot gas linerestriction.
 8. The intelligent thermostat of claim 1, wherein saidprocessing system is configured to identify performance problems due toinefficient compressor operation.
 9. The intelligent thermostat of claim1, wherein said processing system is configured to provide data forplots of energy usage and costs.
 10. The intelligent thermostat of claim1, wherein said processing system is configured to provide data relatedto operation of said refrigerant-cycle system to a remote monitoringcenter.
 11. The intelligent thermostat of claim 1, wherein saidprocessing system is configured to provide data related to operation ofsaid refrigerant-cycle system to a remote monitoring center using powerline networking.
 12. The intelligent thermostat of claim 1, wherein saidprocessing system is configured to provide data related to operation ofsaid refrigerant-cycle system to a remote monitoring center usingbroadband over powerline networking.
 13. The intelligent thermostat ofclaim 1, further comprising an electronically-controlled metering deviceto allow control of refrigerant into an evaporator in anenergy-efficient matter.
 14. The intelligent thermostat of claim 1,wherein said intelligent thermostat is configured with data regarding amaximum expected efficiency for the refrigerant-cycle system.
 15. Theintelligent thermostat of claim 1, wherein said intelligent thermostatis configured with data regarding a type of refrigerant used in therefrigerant-cycle system.
 16. The intelligent thermostat of claim 1,wherein said intelligent thermostat is configured with data regardingthe characteristics of the condenser.
 17. The intelligent thermostat ofclaim 1, wherein said intelligent thermostat is configured with dataregarding the characteristics of the evaporator.
 18. The intelligentthermostat of claim 1, wherein said condenser unit sensors comprise atemperature sensor configured to measure a temperature of therefrigerant in a suction line.
 19. The intelligent thermostat of claim1, wherein said condenser unit sensors comprise a temperature sensorconfigured to measure a temperature of the refrigerant in a liquid line.20. The intelligent thermostat of claim 1, wherein said condenser unitsensors comprise a temperature sensor configured to measure atemperature of the refrigerant in a hot gas line.
 21. The intelligentthermostat of claim 1, wherein said condenser unit sensors comprise apressure sensor configured to measure a pressure of the refrigerant in asuction line.
 22. The intelligent thermostat of claim 1, wherein saidcondenser unit sensors comprise a pressure sensor configured to measurea pressure of the refrigerant in a liquid line.
 23. The intelligentthermostat of claim 1, wherein said condenser unit sensors comprises apressure sensor configured to measure a pressure of the refrigerant in ahot gas line.
 24. The intelligent thermostat of claim 1, wherein saidcondenser unit sensors comprise at least one refrigerant flow sensor.25. The intelligent thermostat of claim 1, wherein said condenser unitsensors comprise at least one refrigerant contaminant sensor.
 26. Theintelligent thermostat of claim 1, wherein said condenser unit sensorscomprises at least one condenser fan tachometer.
 27. The intelligentthermostat of claim 1, wherein said condenser unit sensors comprise atleast one temperature sensor configured to measure a temperature of airout of said condenser.
 28. The intelligent thermostat of claim 1,wherein said evaporator unit sensors comprise a temperature sensor tomeasure a temperature of refrigerant into said evaporator.
 29. Theintelligent thermostat of claim 1, wherein said evaporator unit sensorscomprise a temperature sensor to measure a temperature of refrigerantout of said evaporator.
 30. The intelligent thermostat of claim 1,wherein said evaporator unit sensors comprise a temperature sensor tomeasure a temperature of air into said evaporator.
 31. The intelligentthermostat of claim 1, wherein said evaporator unit sensors comprise atemperature sensor to measure a temperature of air out of saidevaporator.
 32. The intelligent thermostat of claim 1, wherein saidevaporator unit sensors comprise at least one humidity sensor.
 33. Theintelligent thermostat of claim 1, wherein said evaporator unit sensorscomprise at least one air flow sensor.
 34. The intelligent thermostat ofclaim 1, wherein said evaporator unit sensors comprise at least onedifferential pressure sensor.
 35. The intelligent thermostat of claim 1,further comprising a modem, said intelligent thermostat configured toreport performance criteria to a monitoring system using said modem. 36.The intelligent thermostat of claim 1, further comprising a modem, saidintelligent thermostat configured to receive shutdown instructions usingsaid modem.
 37. The intelligent thermostat of claim 1, furthercomprising a modem, said intelligent thermostat configured to receivecommands using said modem.
 38. The intelligent thermostat of claim 1,further comprising a modem, said intelligent thermostat configured toreceive operating instructions using said modem.